From 5a2668150a5aa2b1a5f8e6e80cbde8edf97b1c1b Mon Sep 17 00:00:00 2001
From: Marcono1234 <Marcono1234@users.noreply.github.com>
Date: Wed, 5 Jan 2022 22:15:54 +0100
Subject: [PATCH] Switch to JUnit 5

POM has been configured to compile and run unit tests with Java 11 (because
JUnit 5 requires at least Java 8). However, IDEs might not support different
Java versions for main code and test code.

Another issue is that the proto module uses Google Truth which has JUnit 4 as
transitive dependency.
---
 UserGuide.md                                  |   8 +-
 codegen/pom.xml                               |   4 +-
 .../functional/CodeGenFunctionalTest.java     |   7 +-
 extras/pom.xml                                |   4 +-
 .../gson/graph/GraphAdapterBuilderTest.java   |  30 +-
 .../gson/interceptors/InterceptorTest.java    |  43 +-
 .../PostConstructAdapterFactoryTest.java      |  18 +-
 .../RuntimeTypeAdapterFactoryTest.java        |  52 ++-
 .../typeadapters/UtcDateTypeAdapterTest.java  |  33 +-
 gson/pom.xml                                  |   5 +-
 .../com/google/gson/internal/JavaVersion.java |   2 +-
 .../java/com/google/gson/CommentsTest.java    |   9 +-
 .../DefaultInetAddressTypeAdapterTest.java    |  24 +-
 .../gson/DefaultMapJsonSerializerTest.java    |  15 +-
 ...ExposeAnnotationExclusionStrategyTest.java |  27 +-
 .../com/google/gson/FieldAttributesTest.java  |  36 +-
 .../google/gson/FieldNamingPolicyTest.java    |  26 +-
 .../com/google/gson/GenericArrayTypeTest.java |  27 +-
 .../java/com/google/gson/GsonBuilderTest.java |  75 ++--
 .../test/java/com/google/gson/GsonTest.java   |  25 +-
 .../com/google/gson/GsonTypeAdapterTest.java  |  32 +-
 .../gson/InnerClassExclusionStrategyTest.java |  21 +-
 .../google/gson/JavaSerializationTest.java    |  15 +-
 .../java/com/google/gson/JsonArrayTest.java   |  53 +--
 .../java/com/google/gson/JsonNullTest.java    |  12 +-
 .../java/com/google/gson/JsonObjectTest.java  |  57 ++-
 .../java/com/google/gson/JsonParserTest.java  |  44 +-
 .../com/google/gson/JsonPrimitiveTest.java    | 129 +++---
 .../com/google/gson/JsonStreamParserTest.java |  26 +-
 .../gson/LongSerializationPolicyTest.java     |  26 +-
 .../java/com/google/gson/MixedStreamTest.java |  45 +-
 .../google/gson/ObjectTypeAdapterTest.java    |  21 +-
 .../gson/OverrideCoreTypeAdaptersTest.java    |  15 +-
 .../gson/ParameterizedTypeFixtures.java       |   1 -
 .../google/gson/ParameterizedTypeTest.java    |  22 +-
 .../com/google/gson/ToNumberPolicyTest.java   |  28 +-
 .../gson/VersionExclusionStrategyTest.java    |  16 +-
 .../com/google/gson/common/MoreAsserts.java   |  17 +-
 .../com/google/gson/common/TestTypes.java     |   5 +-
 .../com/google/gson/functional/ArrayTest.java |  99 +++--
 .../functional/CircularReferenceTest.java     |  40 +-
 .../gson/functional/CollectionTest.java       | 138 +++---
 .../gson/functional/ConcurrencyTest.java      |  45 +-
 .../functional/CustomDeserializerTest.java    |  38 +-
 .../gson/functional/CustomSerializerTest.java |  25 +-
 .../functional/CustomTypeAdaptersTest.java    |  94 ++--
 .../functional/DefaultTypeAdaptersTest.java   | 194 +++++---
 .../functional/DelegateTypeAdapterTest.java   |  24 +-
 .../com/google/gson/functional/EnumTest.java  |  57 ++-
 .../functional/EnumWithObfuscatedTest.java    |  19 +-
 .../google/gson/functional/EscapingTest.java  |  29 +-
 .../ExclusionStrategyFunctionalTest.java      |  42 +-
 .../gson/functional/ExposeFieldsTest.java     |  57 ++-
 .../gson/functional/FieldExclusionTest.java   |  22 +-
 .../gson/functional/FieldNamingTest.java      |  23 +-
 .../GsonVersionDiagnosticsTest.java           |  25 +-
 .../gson/functional/InheritanceTest.java      |  72 +--
 .../gson/functional/InstanceCreatorTest.java  |  36 +-
 .../google/gson/functional/InterfaceTest.java |  27 +-
 .../functional/InternationalizationTest.java  |  28 +-
 .../JavaUtilConcurrentAtomicTest.java         |  42 +-
 .../google/gson/functional/JavaUtilTest.java  |  24 +-
 .../JsonAdapterAnnotationOnClassesTest.java   |  40 +-
 .../JsonAdapterAnnotationOnFieldsTest.java    |  44 +-
 ...JsonAdapterSerializerDeserializerTest.java |  18 +-
 .../google/gson/functional/JsonArrayTest.java |  31 +-
 .../gson/functional/JsonParserTest.java       |  39 +-
 .../google/gson/functional/JsonTreeTest.java  |  29 +-
 .../google/gson/functional/LeniencyTest.java  |  18 +-
 .../functional/MapAsArrayTypeAdapterTest.java |  27 +-
 .../com/google/gson/functional/MapTest.java   | 189 +++++---
 .../MoreSpecificTypeSerializationTest.java    |  43 +-
 .../gson/functional/NamingPolicyTest.java     |  69 +--
 .../functional/NullObjectAndFieldTest.java    |  91 ++--
 .../google/gson/functional/ObjectTest.java    | 167 ++++---
 .../functional/ParameterizedTypesTest.java    |  76 ++--
 .../gson/functional/PrettyPrintingTest.java   |  51 ++-
 .../functional/PrimitiveCharacterTest.java    |  17 +-
 .../google/gson/functional/PrimitiveTest.java | 322 +++++++++-----
 .../gson/functional/PrintFormattingTest.java  |  24 +-
 .../gson/functional/RawSerializationTest.java |  31 +-
 .../gson/functional/ReadersWritersTest.java   |  49 ++-
 .../gson/functional/ReflectionAccessTest.java |  19 +-
 .../ReusedTypeVariablesFullyResolveTest.java  |  18 +-
 ...ntimeTypeAdapterFactoryFunctionalTest.java |  17 +-
 .../google/gson/functional/SecurityTest.java  |  45 +-
 .../gson/functional/SerializedNameTest.java   |  16 +-
 .../functional/StreamingTypeAdaptersTest.java |  68 ++-
 .../google/gson/functional/StringTest.java    |  67 ++-
 .../ToNumberPolicyFunctionalTest.java         |  40 +-
 .../gson/functional/TreeTypeAdaptersTest.java |  30 +-
 .../functional/TypeAdapterPrecedenceTest.java |  30 +-
 .../functional/TypeHierarchyAdapterTest.java  |  15 +-
 .../gson/functional/TypeVariableTest.java     |  27 +-
 .../gson/functional/UncategorizedTest.java    |  37 +-
 .../gson/functional/VersioningTest.java       |  46 +-
 .../gson/internal/GsonBuildConfigTest.java    |   8 +-
 .../google/gson/internal/GsonTypesTest.java   |  17 +-
 .../google/gson/internal/JavaVersionTest.java |  25 +-
 .../gson/internal/LazilyParsedNumberTest.java |  17 +-
 .../gson/internal/LinkedTreeMapTest.java      |  50 ++-
 .../UnsafeAllocatorInstantiationTest.java     |  22 +-
 .../bind/DefaultDateTypeAdapterTest.java      |  58 ++-
 .../internal/bind/JsonElementReaderTest.java  |  62 ++-
 .../internal/bind/JsonTreeReaderTest.java     |  12 +-
 .../internal/bind/JsonTreeWriterTest.java     |  58 ++-
 .../bind/RecursiveTypesResolveTest.java       |  36 +-
 .../internal/bind/util/ISO8601UtilsTest.java  |  36 +-
 .../gson/internal/sql/SqlTypesGsonTest.java   |  55 ++-
 .../internal/sql/SqlTypesSupportTest.java     |  10 +-
 .../google/gson/metrics/PerformanceTest.java  | 181 ++++----
 .../google/gson/reflect/TypeTokenTest.java    |  26 +-
 .../regression/JsonAdapterNullSafeTest.java   |  13 +-
 .../com/google/gson/regression/OSGiTest.java  |  16 +-
 .../gson/stream/JsonReaderPathTest.java       |  71 +--
 .../google/gson/stream/JsonReaderTest.java    | 414 ++++++++++++------
 .../google/gson/stream/JsonWriterTest.java    | 123 ++++--
 .../test/resources/testcases-proguard.conf    |   4 +-
 pom.xml                                       |  41 +-
 proto/pom.xml                                 |   4 +-
 .../functional/ProtosWithAnnotationsTest.java |  25 +-
 ...rotosWithComplexAndRepeatedFieldsTest.java |  25 +-
 .../ProtosWithPrimitiveTypesTest.java         |  29 +-
 123 files changed, 3462 insertions(+), 2081 deletions(-)

diff --git a/UserGuide.md b/UserGuide.md
index 331ef27663..429dc23ca7 100644
--- a/UserGuide.md
+++ b/UserGuide.md
@@ -53,13 +53,13 @@ Gson can work with arbitrary Java objects including pre-existing objects that yo
 
 Here are some metrics that we obtained on a desktop (dual opteron, 8GB RAM, 64-bit Ubuntu) running lots of other things along-with the tests. You can rerun these tests by using the class [`PerformanceTest`](gson/src/test/java/com/google/gson/metrics/PerformanceTest.java).
 
-* Strings: Deserialized strings of over 25MB without any problems (see `disabled_testStringDeserializationPerformance` method in `PerformanceTest`)
+* Strings: Deserialized strings of over 25MB without any problems (see `testStringDeserialization` method in `PerformanceTest`)
 * Large collections:
-  * Serialized a collection of 1.4 million objects (see `disabled_testLargeCollectionSerialization` method in `PerformanceTest`)
-  * Deserialized a collection of 87,000 objects (see `disabled_testLargeCollectionDeserialization` in `PerformanceTest`)
+  * Serialized a collection of 1.4 million objects (see `testLargeCollectionSerialization` method in `PerformanceTest`)
+  * Deserialized a collection of 87,000 objects (see `testLargeCollectionDeserialization` in `PerformanceTest`)
 * Gson 1.4 raised the deserialization limit for byte arrays and collection to over 11MB from 80KB.
 
-Note: Delete the `disabled_` prefix to run these tests. We use this prefix to prevent running these tests every time we run JUnit tests.
+Note: Remove the `@Disabled` annotations to run these tests. They are disabled by default to not run them every time we run JUnit tests.
 
 ## <a name="TOC-Gson-Users"></a>Gson Users
 
diff --git a/codegen/pom.xml b/codegen/pom.xml
index 4d232e3a92..8178ad9695 100644
--- a/codegen/pom.xml
+++ b/codegen/pom.xml
@@ -25,8 +25,8 @@
 
   <dependencies>
     <dependency>
-      <groupId>junit</groupId>
-      <artifactId>junit</artifactId>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
   </dependencies>
diff --git a/codegen/src/test/java/com/google/gson/codegen/functional/CodeGenFunctionalTest.java b/codegen/src/test/java/com/google/gson/codegen/functional/CodeGenFunctionalTest.java
index 855ee3faf5..1f66c50a27 100644
--- a/codegen/src/test/java/com/google/gson/codegen/functional/CodeGenFunctionalTest.java
+++ b/codegen/src/test/java/com/google/gson/codegen/functional/CodeGenFunctionalTest.java
@@ -15,11 +15,12 @@
  */
 package com.google.gson.codegen.functional;
 
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public class CodeGenFunctionalTest extends TestCase {
+class CodeGenFunctionalTest {
 
-  public void testGeneratedJson() {
+  @Test
+  void testGeneratedJson() {
     Order order = new Order("toy", 10);
     // TODO: figure out how to access the generated type adapter
   }
diff --git a/extras/pom.xml b/extras/pom.xml
index 0f83b14230..066c79511e 100644
--- a/extras/pom.xml
+++ b/extras/pom.xml
@@ -35,8 +35,8 @@
       <version>1.0</version>
     </dependency>
     <dependency>
-      <groupId>junit</groupId>
-      <artifactId>junit</artifactId>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
   </dependencies>
diff --git a/extras/src/test/java/com/google/gson/graph/GraphAdapterBuilderTest.java b/extras/src/test/java/com/google/gson/graph/GraphAdapterBuilderTest.java
index 43fc6b6991..fa424dc943 100644
--- a/extras/src/test/java/com/google/gson/graph/GraphAdapterBuilderTest.java
+++ b/extras/src/test/java/com/google/gson/graph/GraphAdapterBuilderTest.java
@@ -16,23 +16,21 @@
 
 package com.google.gson.graph;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertSame;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
 
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.reflect.TypeToken;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import org.junit.jupiter.api.Test;
 
-import org.junit.Test;
-
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.reflect.TypeToken;
-
-public final class GraphAdapterBuilderTest {
+class GraphAdapterBuilderTest {
   @Test
-  public void testSerialization() {
+  void testSerialization() {
     Roshambo rock = new Roshambo("ROCK");
     Roshambo scissors = new Roshambo("SCISSORS");
     Roshambo paper = new Roshambo("PAPER");
@@ -53,7 +51,7 @@ public void testSerialization() {
   }
 
   @Test
-  public void testDeserialization() {
+  void testDeserialization() {
     String json = "{'0x1':{'name':'ROCK','beats':'0x2'}," +
         "'0x2':{'name':'SCISSORS','beats':'0x3'}," +
         "'0x3':{'name':'PAPER','beats':'0x1'}}";
@@ -74,7 +72,7 @@ public void testDeserialization() {
   }
 
   @Test
-  public void testDeserializationDirectSelfReference() {
+  void testDeserializationDirectSelfReference() {
     String json = "{'0x1':{'name':'SUICIDE','beats':'0x1'}}";
 
     GsonBuilder gsonBuilder = new GsonBuilder();
@@ -89,7 +87,7 @@ public void testDeserializationDirectSelfReference() {
   }
 
   @Test
-  public void testSerializeListOfLists() {
+  void testSerializeListOfLists() {
     Type listOfListsType = new TypeToken<List<List<?>>>() {}.getType();
     Type listOfAnyType = new TypeToken<List<?>>() {}.getType();
 
@@ -109,7 +107,7 @@ public void testSerializeListOfLists() {
   }
 
   @Test
-  public void testDeserializeListOfLists() {
+  void testDeserializeListOfLists() {
     Type listOfAnyType = new TypeToken<List<?>>() {}.getType();
     Type listOfListsType = new TypeToken<List<List<?>>>() {}.getType();
 
@@ -127,7 +125,7 @@ public void testDeserializeListOfLists() {
   }
 
   @Test
-  public void testSerializationWithMultipleTypes() {
+  void testSerializationWithMultipleTypes() {
     Company google = new Company("Google");
     new Employee("Jesse", google);
     new Employee("Joel", google);
@@ -146,7 +144,7 @@ public void testSerializationWithMultipleTypes() {
   }
 
   @Test
-  public void testDeserializationWithMultipleTypes() {
+  void testDeserializationWithMultipleTypes() {
     GsonBuilder gsonBuilder = new GsonBuilder();
     new GraphAdapterBuilder()
         .addType(Company.class)
diff --git a/extras/src/test/java/com/google/gson/interceptors/InterceptorTest.java b/extras/src/test/java/com/google/gson/interceptors/InterceptorTest.java
index 0aab6598c3..1bf6958812 100644
--- a/extras/src/test/java/com/google/gson/interceptors/InterceptorTest.java
+++ b/extras/src/test/java/com/google/gson/interceptors/InterceptorTest.java
@@ -15,6 +15,9 @@
  */
 package com.google.gson.interceptors;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonParseException;
@@ -29,51 +32,56 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for {@link Intercept} and {@link JsonPostDeserializer}.
  *
  * @author Inderjeet Singh
  */
-public final class InterceptorTest extends TestCase {
+class InterceptorTest {
 
   private Gson gson;
 
-  @Override
-  public void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     this.gson = new GsonBuilder()
         .registerTypeAdapterFactory(new InterceptorFactory())
         .enableComplexMapKeySerialization()
         .create();
   }
 
-  public void testExceptionsPropagated() {
+  @Test
+  void testExceptionsPropagated() {
     try {
       gson.fromJson("{}", User.class);
       fail();
     } catch (JsonParseException expected) {}
   }
 
-  public void testTopLevelClass() {
+  @Test
+  void testTopLevelClass() {
     User user = gson.fromJson("{name:'bob',password:'pwd'}", User.class);
     assertEquals(User.DEFAULT_EMAIL, user.email);
   }
 
-  public void testList() {
+  @Test
+  void testList() {
     List<User> list = gson.fromJson("[{name:'bob',password:'pwd'}]", new TypeToken<List<User>>(){}.getType());
     User user = list.get(0);
     assertEquals(User.DEFAULT_EMAIL, user.email);
   }
 
-  public void testCollection() {
+  @Test
+  void testCollection() {
     Collection<User> list = gson.fromJson("[{name:'bob',password:'pwd'}]", new TypeToken<Collection<User>>(){}.getType());
     User user = list.iterator().next();
     assertEquals(User.DEFAULT_EMAIL, user.email);
   }
 
-  public void testMapKeyAndValues() {
+  @Test
+  void testMapKeyAndValues() {
     Type mapType = new TypeToken<Map<User, Address>>(){}.getType();
     try {
       gson.fromJson("[[{name:'bob',password:'pwd'},{}]]", mapType);
@@ -86,12 +94,14 @@ public void testMapKeyAndValues() {
     assertEquals(Address.DEFAULT_FIRST_LINE, entry.getValue().firstLine);
   }
 
-  public void testField() {
+  @Test
+  void testField() {
     UserGroup userGroup = gson.fromJson("{user:{name:'bob',password:'pwd'}}", UserGroup.class);
     assertEquals(User.DEFAULT_EMAIL, userGroup.user.email);
   }
 
-  public void testCustomTypeAdapter() {
+  @Test
+  void testCustomTypeAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(User.class, new TypeAdapter<User>() {
           @Override public void write(JsonWriter out, User value) throws IOException {
@@ -114,7 +124,8 @@ public void testCustomTypeAdapter() {
     assertEquals(User.DEFAULT_EMAIL, userGroup.user.email);
   }
 
-  public void testDirectInvocationOfTypeAdapter() throws Exception {
+  @Test
+  void testDirectInvocationOfTypeAdapter() throws Exception {
     TypeAdapter<UserGroup> adapter = gson.getAdapter(UserGroup.class);
     UserGroup userGroup = adapter.fromJson("{\"user\":{\"name\":\"bob\",\"password\":\"pwd\"}}");
     assertEquals(User.DEFAULT_EMAIL, userGroup.user.email);
@@ -140,7 +151,8 @@ public User(String name, String password) {
     }
   }
 
-  public static final class UserValidator implements JsonPostDeserializer<User> {
+  static final class UserValidator implements JsonPostDeserializer<User> {
+    @Override
     public void postDeserialize(User user) {
       if (user.name == null || user.password == null) {
         throw new JsonSyntaxException("name and password are required fields.");
@@ -160,7 +172,8 @@ private static final class Address {
     String zip;
   }
 
-  public static final class AddressValidator implements JsonPostDeserializer<Address> {
+  static final class AddressValidator implements JsonPostDeserializer<Address> {
+    @Override
     public void postDeserialize(Address address) {
       if (address.city == null || address.state == null || address.zip == null) {
         throw new JsonSyntaxException("Address city, state and zip are required fields.");
diff --git a/extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java b/extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java
index 7bd0a520d9..7bae1bbcfd 100644
--- a/extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java
+++ b/extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java
@@ -16,18 +16,19 @@
 
 package com.google.gson.typeadapters;
 
-import javax.annotation.PostConstruct;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-
-import junit.framework.TestCase;
-
 import java.util.Arrays;
 import java.util.List;
+import javax.annotation.PostConstruct;
+import org.junit.jupiter.api.Test;
 
-public class PostConstructAdapterFactoryTest extends TestCase {
-    public void test() throws Exception {
+class PostConstructAdapterFactoryTest {
+    @Test
+    void test() throws Exception {
         Gson gson = new GsonBuilder()
                 .registerTypeAdapterFactory(new PostConstructAdapterFactory())
                 .create();
@@ -40,7 +41,8 @@ public void test() throws Exception {
         }
     }
 
-    public void testList() {
+    @Test
+    void testList() {
         MultipleSandwiches sandwiches = new MultipleSandwiches(Arrays.asList(
             new Sandwich("white", "cheddar"),
             new Sandwich("whole wheat", "swiss")));
@@ -70,6 +72,7 @@ public Sandwich(String bread, String cheese) {
             }
         }
 
+        @Override
         public boolean equals(Object o) {
             if (o == this) {
                 return true;
@@ -95,6 +98,7 @@ public MultipleSandwiches(List<Sandwich> sandwiches) {
             this.sandwiches = sandwiches;
         }
 
+        @Override
         public boolean equals(Object o) {
             if (o == this) {
                 return true;
diff --git a/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java b/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
index 8c62bef7f4..af23bba9cc 100644
--- a/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
+++ b/extras/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
@@ -16,15 +16,21 @@
 
 package com.google.gson.typeadapters;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonParseException;
 import com.google.gson.TypeAdapterFactory;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class RuntimeTypeAdapterFactoryTest extends TestCase {
+class RuntimeTypeAdapterFactoryTest {
 
-  public void testRuntimeTypeAdapter() {
+  @Test
+  void testRuntimeTypeAdapter() {
     RuntimeTypeAdapterFactory<BillingInstrument> rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class)
         .registerSubtype(CreditCard.class);
@@ -41,7 +47,8 @@ public void testRuntimeTypeAdapter() {
     assertTrue(deserialized instanceof CreditCard);
   }
 
-  public void testRuntimeTypeIsBaseType() {
+  @Test
+  void testRuntimeTypeIsBaseType() {
     TypeAdapterFactory rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class)
         .registerSubtype(BillingInstrument.class);
@@ -57,7 +64,8 @@ public void testRuntimeTypeIsBaseType() {
     assertEquals("Jesse", deserialized.ownerName);
   }
 
-  public void testNullBaseType() {
+  @Test
+  void testNullBaseType() {
     try {
       RuntimeTypeAdapterFactory.of(null);
       fail();
@@ -65,7 +73,8 @@ public void testNullBaseType() {
     }
   }
 
-  public void testNullTypeFieldName() {
+  @Test
+  void testNullTypeFieldName() {
     try {
       RuntimeTypeAdapterFactory.of(BillingInstrument.class, null);
       fail();
@@ -73,7 +82,8 @@ public void testNullTypeFieldName() {
     }
   }
 
-  public void testNullSubtype() {
+  @Test
+  void testNullSubtype() {
     RuntimeTypeAdapterFactory<BillingInstrument> rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class);
     try {
@@ -83,7 +93,8 @@ public void testNullSubtype() {
     }
   }
 
-  public void testNullLabel() {
+  @Test
+  void testNullLabel() {
     RuntimeTypeAdapterFactory<BillingInstrument> rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class);
     try {
@@ -93,7 +104,8 @@ public void testNullLabel() {
     }
   }
 
-  public void testDuplicateSubtype() {
+  @Test
+  void testDuplicateSubtype() {
     RuntimeTypeAdapterFactory<BillingInstrument> rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class);
     rta.registerSubtype(CreditCard.class, "CC");
@@ -104,7 +116,8 @@ public void testDuplicateSubtype() {
     }
   }
 
-  public void testDuplicateLabel() {
+  @Test
+  void testDuplicateLabel() {
     RuntimeTypeAdapterFactory<BillingInstrument> rta = RuntimeTypeAdapterFactory.of(
         BillingInstrument.class);
     rta.registerSubtype(CreditCard.class, "CC");
@@ -115,7 +128,8 @@ public void testDuplicateLabel() {
     }
   }
 
-  public void testDeserializeMissingTypeField() {
+  @Test
+  void testDeserializeMissingTypeField() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class)
         .registerSubtype(CreditCard.class);
     Gson gson = new GsonBuilder()
@@ -128,7 +142,8 @@ public void testDeserializeMissingTypeField() {
     }
   }
 
-  public void testDeserializeMissingSubtype() {
+  @Test
+  void testDeserializeMissingSubtype() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class)
         .registerSubtype(BankTransfer.class);
     Gson gson = new GsonBuilder()
@@ -141,7 +156,8 @@ public void testDeserializeMissingSubtype() {
     }
   }
 
-  public void testSerializeMissingSubtype() {
+  @Test
+  void testSerializeMissingSubtype() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class)
         .registerSubtype(BankTransfer.class);
     Gson gson = new GsonBuilder()
@@ -154,7 +170,8 @@ public void testSerializeMissingSubtype() {
     }
   }
 
-  public void testSerializeCollidingTypeFieldName() {
+  @Test
+  void testSerializeCollidingTypeFieldName() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class, "cvv")
         .registerSubtype(CreditCard.class);
     Gson gson = new GsonBuilder()
@@ -167,13 +184,14 @@ public void testSerializeCollidingTypeFieldName() {
     }
   }
 
-  public void testSerializeWrappedNullValue() {
+  @Test
+  void testSerializeWrappedNullValue() {
     TypeAdapterFactory billingAdapter = RuntimeTypeAdapterFactory.of(BillingInstrument.class)
         .registerSubtype(CreditCard.class)
-        .registerSubtype(BankTransfer.class);    
+        .registerSubtype(BankTransfer.class);
     Gson gson = new GsonBuilder()
         .registerTypeAdapterFactory(billingAdapter)
-        .create();    
+        .create();
     String serialized = gson.toJson(new BillingInstrumentWrapper(null), BillingInstrumentWrapper.class);
     BillingInstrumentWrapper deserialized = gson.fromJson(serialized, BillingInstrumentWrapper.class);
     assertNull(deserialized.instrument);
diff --git a/extras/src/test/java/com/google/gson/typeadapters/UtcDateTypeAdapterTest.java b/extras/src/test/java/com/google/gson/typeadapters/UtcDateTypeAdapterTest.java
index 56e54290cf..13c8246977 100644
--- a/extras/src/test/java/com/google/gson/typeadapters/UtcDateTypeAdapterTest.java
+++ b/extras/src/test/java/com/google/gson/typeadapters/UtcDateTypeAdapterTest.java
@@ -16,31 +16,34 @@
 
 package com.google.gson.typeadapters;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonParseException;
 import java.text.SimpleDateFormat;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.Locale;
 import java.util.TimeZone;
+import org.junit.jupiter.api.Test;
 
-import com.google.gson.JsonParseException;
-import junit.framework.TestCase;
-
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-
-public final class UtcDateTypeAdapterTest extends TestCase {
+class UtcDateTypeAdapterTest {
   private final Gson gson = new GsonBuilder()
     .registerTypeAdapter(Date.class, new UtcDateTypeAdapter())
     .create();
 
-  public void testLocalTimeZone() {
+  @Test
+  void testLocalTimeZone() {
     Date expected = new Date();
     String json = gson.toJson(expected);
     Date actual = gson.fromJson(json, Date.class);
     assertEquals(expected.getTime(), actual.getTime());
   }
 
-  public void testDifferentTimeZones() {
+  @Test
+  void testDifferentTimeZones() {
     for (String timeZone : TimeZone.getAvailableIDs()) {
       Calendar cal = Calendar.getInstance(TimeZone.getTimeZone(timeZone));
       Date expected = cal.getTime();
@@ -55,14 +58,16 @@ public void testDifferentTimeZones() {
    * JDK 1.7 introduced support for XXX format to indicate UTC date. But Android is older JDK.
    * We want to make sure that this date is parseable in Android.
    */
-  public void testUtcDatesOnJdkBefore1_7() {
+  @Test
+  void testUtcDatesOnJdkBefore1_7() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Date.class, new UtcDateTypeAdapter())
       .create();
     gson.fromJson("'2014-12-05T04:00:00.000Z'", Date.class);
   }
 
-  public void testUtcWithJdk7Default() {
+  @Test
+  void testUtcWithJdk7Default() {
     Date expected = new Date();
     SimpleDateFormat iso8601Format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX", Locale.US);
     iso8601Format.setTimeZone(TimeZone.getTimeZone("UTC"));
@@ -73,12 +78,14 @@ public void testUtcWithJdk7Default() {
     assertEquals(expected.getTime(), actual.getTime());
   }
 
-  public void testNullDateSerialization() {
+  @Test
+  void testNullDateSerialization() {
     String json = gson.toJson(null, Date.class);
     assertEquals("null", json);
   }
 
-  public void testWellFormedParseException() {
+  @Test
+  void testWellFormedParseException() {
     try {
       gson.fromJson("2017-06-20T14:32:30", Date.class);
       fail("No exception");
diff --git a/gson/pom.xml b/gson/pom.xml
index c1be6a920b..d78588b575 100644
--- a/gson/pom.xml
+++ b/gson/pom.xml
@@ -21,8 +21,8 @@
 
   <dependencies>
     <dependency>
-      <groupId>junit</groupId>
-      <artifactId>junit</artifactId>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
   </dependencies>
@@ -50,7 +50,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-surefire-plugin</artifactId>
-        <version>3.0.0-M5</version>
         <configuration>
           <!-- Deny illegal access, this is required for ReflectionAccessTest -->
           <!-- Requires Java >= 9; Important: In case future Java versions 
diff --git a/gson/src/main/java/com/google/gson/internal/JavaVersion.java b/gson/src/main/java/com/google/gson/internal/JavaVersion.java
index fab1b7c274..c300106a7f 100644
--- a/gson/src/main/java/com/google/gson/internal/JavaVersion.java
+++ b/gson/src/main/java/com/google/gson/internal/JavaVersion.java
@@ -37,7 +37,7 @@ static int getMajorJavaVersion(String javaVersion) {
       version = extractBeginningInt(javaVersion);
     }
     if (version == -1) {
-      return 6;  // Choose minimum supported JDK version as default
+      return 7;  // Choose minimum supported JDK version as default
     }
     return version;
   }
diff --git a/gson/src/test/java/com/google/gson/CommentsTest.java b/gson/src/test/java/com/google/gson/CommentsTest.java
index 306e5aff33..aa3e57c1ee 100644
--- a/gson/src/test/java/com/google/gson/CommentsTest.java
+++ b/gson/src/test/java/com/google/gson/CommentsTest.java
@@ -16,20 +16,23 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.reflect.TypeToken;
 import java.util.Arrays;
 import java.util.List;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * @author Jesse Wilson
  */
-public final class CommentsTest extends TestCase {
+class CommentsTest {
 
   /**
    * Test for issue 212.
    */
-  public void testParseComments() {
+  @Test
+  void testParseComments() {
     String json = "[\n"
         + "  // this is a comment\n"
         + "  \"a\",\n"
diff --git a/gson/src/test/java/com/google/gson/DefaultInetAddressTypeAdapterTest.java b/gson/src/test/java/com/google/gson/DefaultInetAddressTypeAdapterTest.java
index 6b853f5de8..b43880f64f 100644
--- a/gson/src/test/java/com/google/gson/DefaultInetAddressTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/DefaultInetAddressTypeAdapterTest.java
@@ -16,30 +16,32 @@
 
 package com.google.gson;
 
-import java.net.InetAddress;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import junit.framework.TestCase;
+import java.net.InetAddress;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for the default serializer/deserializer for the {@code InetAddress} type.
  * 
  * @author Joel Leitch
  */
-public class DefaultInetAddressTypeAdapterTest extends TestCase {
+class DefaultInetAddressTypeAdapterTest {
   private Gson gson;
-  
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
-  
-  public void testInetAddressSerializationAndDeserialization() throws Exception {
+
+  @Test
+  void testInetAddressSerializationAndDeserialization() throws Exception {
     InetAddress address = InetAddress.getByName("8.8.8.8");
     String jsonAddress = gson.toJson(address);
     assertEquals("\"8.8.8.8\"", jsonAddress);
-    
+
     InetAddress value = gson.fromJson(jsonAddress, InetAddress.class);
     assertEquals(value, address);
-  } 
+  }
 }
diff --git a/gson/src/test/java/com/google/gson/DefaultMapJsonSerializerTest.java b/gson/src/test/java/com/google/gson/DefaultMapJsonSerializerTest.java
index 5c06195358..64709297b2 100644
--- a/gson/src/test/java/com/google/gson/DefaultMapJsonSerializerTest.java
+++ b/gson/src/test/java/com/google/gson/DefaultMapJsonSerializerTest.java
@@ -16,11 +16,13 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.reflect.TypeToken;
 import java.lang.reflect.Type;
 import java.util.HashMap;
 import java.util.Map;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for the default JSON map serialization object located in the
@@ -28,10 +30,11 @@
  *
  * @author Joel Leitch
  */
-public class DefaultMapJsonSerializerTest extends TestCase {
+class DefaultMapJsonSerializerTest {
   private Gson gson = new Gson();
 
-  public void testEmptyMapNoTypeSerialization() {
+  @Test
+  void testEmptyMapNoTypeSerialization() {
     Map<String, String> emptyMap = new HashMap<String, String>();
     JsonElement element = gson.toJsonTree(emptyMap, emptyMap.getClass());
     assertTrue(element instanceof JsonObject);
@@ -39,7 +42,8 @@ public void testEmptyMapNoTypeSerialization() {
     assertTrue(emptyMapJsonObject.entrySet().isEmpty());
   }
 
-  public void testEmptyMapSerialization() {
+  @Test
+  void testEmptyMapSerialization() {
     Type mapType = new TypeToken<Map<String, String>>() { }.getType();
     Map<String, String> emptyMap = new HashMap<String, String>();
     JsonElement element = gson.toJsonTree(emptyMap, mapType);
@@ -49,7 +53,8 @@ public void testEmptyMapSerialization() {
     assertTrue(emptyMapJsonObject.entrySet().isEmpty());
   }
 
-  public void testNonEmptyMapSerialization() {
+  @Test
+  void testNonEmptyMapSerialization() {
     Type mapType = new TypeToken<Map<String, String>>() { }.getType();
     Map<String, String> myMap = new HashMap<String, String>();
     String key = "key1";
diff --git a/gson/src/test/java/com/google/gson/ExposeAnnotationExclusionStrategyTest.java b/gson/src/test/java/com/google/gson/ExposeAnnotationExclusionStrategyTest.java
index dd8a7a926b..8cebfb92bf 100644
--- a/gson/src/test/java/com/google/gson/ExposeAnnotationExclusionStrategyTest.java
+++ b/gson/src/test/java/com/google/gson/ExposeAnnotationExclusionStrategyTest.java
@@ -16,51 +16,58 @@
 
 package com.google.gson;
 
-import com.google.gson.annotations.Expose;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import com.google.gson.annotations.Expose;
 import com.google.gson.internal.Excluder;
-import junit.framework.TestCase;
-
 import java.lang.reflect.Field;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for GsonBuilder.REQUIRE_EXPOSE_DESERIALIZE.
  *
  * @author Joel Leitch
  */
-public class ExposeAnnotationExclusionStrategyTest extends TestCase {
+class ExposeAnnotationExclusionStrategyTest {
   private Excluder excluder = Excluder.DEFAULT.excludeFieldsWithoutExposeAnnotation();
 
-  public void testNeverSkipClasses() throws Exception {
+  @Test
+  void testNeverSkipClasses() throws Exception {
     assertFalse(excluder.excludeClass(MockObject.class, true));
     assertFalse(excluder.excludeClass(MockObject.class, false));
   }
 
-  public void testSkipNonAnnotatedFields() throws Exception {
+  @Test
+  void testSkipNonAnnotatedFields() throws Exception {
     Field f = createFieldAttributes("hiddenField");
     assertTrue(excluder.excludeField(f, true));
     assertTrue(excluder.excludeField(f, false));
   }
 
-  public void testSkipExplicitlySkippedFields() throws Exception {
+  @Test
+  void testSkipExplicitlySkippedFields() throws Exception {
     Field f = createFieldAttributes("explicitlyHiddenField");
     assertTrue(excluder.excludeField(f, true));
     assertTrue(excluder.excludeField(f, false));
   }
 
-  public void testNeverSkipExposedAnnotatedFields() throws Exception {
+  @Test
+  void testNeverSkipExposedAnnotatedFields() throws Exception {
     Field f = createFieldAttributes("exposedField");
     assertFalse(excluder.excludeField(f, true));
     assertFalse(excluder.excludeField(f, false));
   }
 
-  public void testNeverSkipExplicitlyExposedAnnotatedFields() throws Exception {
+  @Test
+  void testNeverSkipExplicitlyExposedAnnotatedFields() throws Exception {
     Field f = createFieldAttributes("explicitlyExposedField");
     assertFalse(excluder.excludeField(f, true));
     assertFalse(excluder.excludeField(f, false));
   }
 
-  public void testDifferentSerializeAndDeserializeField() throws Exception {
+  @Test
+  void testDifferentSerializeAndDeserializeField() throws Exception {
     Field f = createFieldAttributes("explicitlyDifferentModeField");
     assertFalse(excluder.excludeField(f, true));
     assertTrue(excluder.excludeField(f, false));
diff --git a/gson/src/test/java/com/google/gson/FieldAttributesTest.java b/gson/src/test/java/com/google/gson/FieldAttributesTest.java
index a032266bbf..5e73b91ae2 100644
--- a/gson/src/test/java/com/google/gson/FieldAttributesTest.java
+++ b/gson/src/test/java/com/google/gson/FieldAttributesTest.java
@@ -16,13 +16,17 @@
 
 package com.google.gson;
 
-import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
+import com.google.gson.reflect.TypeToken;
 import java.lang.reflect.Modifier;
 import java.lang.reflect.Type;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for the {@link FieldAttributes} class.
@@ -30,28 +34,29 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class FieldAttributesTest extends TestCase {
+class FieldAttributesTest {
   private FieldAttributes fieldAttributes;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     fieldAttributes = new FieldAttributes(Foo.class.getField("bar"));
   }
 
-  @SuppressWarnings("unused")
-  public void testNullField() throws Exception {
+  @Test
+  void testNullField() throws Exception {
     try {
       new FieldAttributes(null);
       fail("Field parameter can not be null");
     } catch (NullPointerException expected) { }
   }
 
-  public void testDeclaringClass() throws Exception {
+  @Test
+  void testDeclaringClass() throws Exception {
     assertEquals(Foo.class, fieldAttributes.getDeclaringClass());
   }
 
-  public void testModifiers() throws Exception {
+  @Test
+  void testModifiers() throws Exception {
     assertFalse(fieldAttributes.hasModifier(Modifier.STATIC));
     assertFalse(fieldAttributes.hasModifier(Modifier.FINAL));
     assertFalse(fieldAttributes.hasModifier(Modifier.ABSTRACT));
@@ -62,15 +67,18 @@ public void testModifiers() throws Exception {
     assertTrue(fieldAttributes.hasModifier(Modifier.TRANSIENT));
   }
 
-  public void testIsSynthetic() throws Exception {
+  @Test
+  void testIsSynthetic() throws Exception {
     assertFalse(fieldAttributes.isSynthetic());
   }
 
-  public void testName() throws Exception {
+  @Test
+  void testName() throws Exception {
     assertEquals("bar", fieldAttributes.getName());
   }
 
-  public void testDeclaredTypeAndClass() throws Exception {
+  @Test
+  void testDeclaredTypeAndClass() throws Exception {
     Type expectedType = new TypeToken<List<String>>() {}.getType();
     assertEquals(expectedType, fieldAttributes.getDeclaredType());
     assertEquals(List.class, fieldAttributes.getDeclaredClass());
diff --git a/gson/src/test/java/com/google/gson/FieldNamingPolicyTest.java b/gson/src/test/java/com/google/gson/FieldNamingPolicyTest.java
index 4d4c716b1e..854203daa7 100644
--- a/gson/src/test/java/com/google/gson/FieldNamingPolicyTest.java
+++ b/gson/src/test/java/com/google/gson/FieldNamingPolicyTest.java
@@ -1,19 +1,19 @@
 package com.google.gson;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+
 import java.lang.reflect.Field;
 import java.util.Locale;
-import org.junit.Test;
-import com.google.gson.functional.FieldNamingTest;
+import org.junit.jupiter.api.Test;
 
 /**
  * Performs tests directly against {@link FieldNamingPolicy}; for integration tests
  * see {@link FieldNamingTest}.
  */
-public class FieldNamingPolicyTest {
+class FieldNamingPolicyTest {
   @Test
-  public void testSeparateCamelCase() {
+  void testSeparateCamelCase() {
     // Map from original -> expected
     String[][] argumentPairs =  {
       { "a", "a" },
@@ -33,7 +33,7 @@ public void testSeparateCamelCase() {
   }
 
   @Test
-  public void testUpperCaseFirstLetter() {
+  void testUpperCaseFirstLetter() {
     // Map from original -> expected
     String[][] argumentPairs =  {
       { "a", "A" },
@@ -59,7 +59,7 @@ public void testUpperCaseFirstLetter() {
    * Upper casing policies should be unaffected by default Locale.
    */
   @Test
-  public void testUpperCasingLocaleIndependent() throws Exception {
+  void testUpperCasingLocaleIndependent() throws Exception {
     class Dummy {
       @SuppressWarnings("unused")
       int i;
@@ -81,11 +81,11 @@ class Dummy {
 
     try {
       // Verify that default Locale has different case conversion rules
-      assertNotEquals("Test setup is broken", expected, name.toUpperCase());
+      assertNotEquals(expected, name.toUpperCase(), "Test setup is broken");
 
       for (FieldNamingPolicy policy : policies) {
         // Should ignore default Locale
-        assertEquals("Unexpected conversion for " + policy, expected, policy.translateName(field));
+        assertEquals(expected, policy.translateName(field), "Unexpected conversion for " + policy);
       }
     } finally {
         Locale.setDefault(oldLocale);
@@ -96,7 +96,7 @@ class Dummy {
    * Lower casing policies should be unaffected by default Locale.
    */
   @Test
-  public void testLowerCasingLocaleIndependent() throws Exception {
+  void testLowerCasingLocaleIndependent() throws Exception {
     class Dummy {
       @SuppressWarnings("unused")
       int I;
@@ -118,11 +118,11 @@ class Dummy {
 
     try {
       // Verify that default Locale has different case conversion rules
-      assertNotEquals("Test setup is broken", expected, name.toLowerCase());
+      assertNotEquals(expected, name.toLowerCase(), "Test setup is broken");
 
       for (FieldNamingPolicy policy : policies) {
         // Should ignore default Locale
-        assertEquals("Unexpected conversion for " + policy, expected, policy.translateName(field));
+        assertEquals(expected, policy.translateName(field), "Unexpected conversion for " + policy);
       }
     } finally {
         Locale.setDefault(oldLocale);
diff --git a/gson/src/test/java/com/google/gson/GenericArrayTypeTest.java b/gson/src/test/java/com/google/gson/GenericArrayTypeTest.java
index 42acb8a2d9..4433e766ce 100644
--- a/gson/src/test/java/com/google/gson/GenericArrayTypeTest.java
+++ b/gson/src/test/java/com/google/gson/GenericArrayTypeTest.java
@@ -16,14 +16,16 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import com.google.gson.common.MoreAsserts;
 import com.google.gson.internal.$Gson$Types;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.GenericArrayType;
 import java.lang.reflect.Type;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for the {@code GenericArrayType}s created by the {@link $Gson$Types} class.
@@ -31,26 +33,27 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class GenericArrayTypeTest extends TestCase {
+class GenericArrayTypeTest {
   private GenericArrayType ourType;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     ourType = $Gson$Types.arrayOf($Gson$Types.newParameterizedTypeWithOwner(null, List.class, String.class));
   }
 
-  public void testOurTypeFunctionality() throws Exception {
+  @Test
+  void testOurTypeFunctionality() throws Exception {
     Type parameterizedType = new TypeToken<List<String>>() {}.getType();
     Type genericArrayType = new TypeToken<List<String>[]>() {}.getType();
 
-    assertEquals(parameterizedType, ourType.getGenericComponentType());
-    assertEquals(genericArrayType, ourType);
-    assertEquals(genericArrayType.hashCode(), ourType.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(parameterizedType, ourType.getGenericComponentType());
+    MoreAsserts.assertEqualsAndHashCode(genericArrayType, ourType);
   }
 
-  public void testNotEquals() throws Exception {
+  @Test
+  void testNotEquals() throws Exception {
     Type differentGenericArrayType = new TypeToken<List<String>[][]>() {}.getType();
+    // Explicitly test `equals` implementation
     assertFalse(differentGenericArrayType.equals(ourType));
     assertFalse(ourType.equals(differentGenericArrayType));
   }
diff --git a/gson/src/test/java/com/google/gson/GsonBuilderTest.java b/gson/src/test/java/com/google/gson/GsonBuilderTest.java
index d1fd0d4fc2..be5792adba 100644
--- a/gson/src/test/java/com/google/gson/GsonBuilderTest.java
+++ b/gson/src/test/java/com/google/gson/GsonBuilderTest.java
@@ -16,53 +16,68 @@
 
 package com.google.gson;
 
-import java.lang.reflect.Modifier;
-import java.lang.reflect.Type;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.lang.reflect.Modifier;
+import java.util.Objects;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 /**
  * Unit tests for {@link GsonBuilder}.
  *
  * @author Inderjeet Singh
  */
-public class GsonBuilderTest extends TestCase {
-  private static final TypeAdapter<Object> NULL_TYPE_ADAPTER = new TypeAdapter<Object>() {
-    @Override public void write(JsonWriter out, Object value) {
-      throw new AssertionError();
-    }
-    @Override public Object read(JsonReader in) {
-      throw new AssertionError();
-    }
-  };
-
-  public void testCreatingMoreThanOnce() {
+class GsonBuilderTest {
+  @Test
+  void testCreatingMoreThanOnce() {
     GsonBuilder builder = new GsonBuilder();
     builder.create();
     builder.create();
   }
 
-  public void testExcludeFieldsWithModifiers() {
+  @Test
+  void testExcludeFieldsWithModifiers() {
     Gson gson = new GsonBuilder()
         .excludeFieldsWithModifiers(Modifier.VOLATILE, Modifier.PRIVATE)
         .create();
     assertEquals("{\"d\":\"d\"}", gson.toJson(new HasModifiers()));
   }
 
-  public void testRegisterTypeAdapterForCoreType() {
-    Type[] types = {
-        byte.class,
-        int.class,
-        double.class,
-        Short.class,
-        Long.class,
-        String.class,
-    };
-    for (Type type : types) {
-      new GsonBuilder().registerTypeAdapter(type, NULL_TYPE_ADAPTER);
+  @ParameterizedTest
+  @ValueSource(classes = {
+    byte.class,
+    int.class,
+    double.class,
+    Short.class,
+    Long.class,
+    String.class,
+  })
+  void testRegisterTypeAdapterForCoreType(Class<?> type) {
+    Gson gson = new GsonBuilder()
+        .registerTypeAdapter(type, new TypeAdapter<Object>() {
+          @Override public void write(JsonWriter out, Object value) throws IOException {
+            out.value("custom-write: " + Objects.toString(value));
+          }
+          @Override public Object read(JsonReader in) throws IOException {
+            throw new IOException("custom-read: " + in.nextString());
+          }
+        })
+        .create();
+
+    String actualJson = gson.toJson(null, type);
+    assertEquals("\"custom-write: null\"", actualJson);
+
+    try {
+      gson.fromJson("\"test\"", type);
+      fail();
+    } catch (JsonSyntaxException e) {
+      assertEquals("custom-read: test", e.getCause().getMessage());
     }
   }
 
@@ -74,7 +89,8 @@ static class HasModifiers {
     String d = "d";
   }
 
-  public void testTransientFieldExclusion() {
+  @Test
+  void testTransientFieldExclusion() {
     Gson gson = new GsonBuilder()
         .excludeFieldsWithModifiers()
         .create();
@@ -85,7 +101,8 @@ static class HasTransients {
     transient String a = "a";
   }
 
-  public void testDisableJdkUnsafe() {
+  @Test
+  void testDisableJdkUnsafe() {
     Gson gson = new GsonBuilder()
         .disableJdkUnsafe()
         .create();
diff --git a/gson/src/test/java/com/google/gson/GsonTest.java b/gson/src/test/java/com/google/gson/GsonTest.java
index 186ceec9bd..bd5ebf393e 100644
--- a/gson/src/test/java/com/google/gson/GsonTest.java
+++ b/gson/src/test/java/com/google/gson/GsonTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.internal.Excluder;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
@@ -28,14 +31,14 @@
 import java.text.DateFormat;
 import java.util.ArrayList;
 import java.util.HashMap;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for {@link Gson}.
  *
  * @author Ryan Harter
  */
-public final class GsonTest extends TestCase {
+class GsonTest {
 
   private static final Excluder CUSTOM_EXCLUDER = Excluder.DEFAULT
       .excludeFieldsWithoutExposeAnnotation()
@@ -50,7 +53,8 @@ public final class GsonTest extends TestCase {
   private static final ToNumberStrategy CUSTOM_OBJECT_TO_NUMBER_STRATEGY = ToNumberPolicy.DOUBLE;
   private static final ToNumberStrategy CUSTOM_NUMBER_TO_NUMBER_STRATEGY = ToNumberPolicy.LAZILY_PARSED_NUMBER;
 
-  public void testOverridesDefaultExcluder() {
+  @Test
+  void testOverridesDefaultExcluder() {
     Gson gson = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
         true, true, false, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
@@ -64,7 +68,8 @@ public void testOverridesDefaultExcluder() {
     assertEquals(false, gson.htmlSafe());
   }
 
-  public void testClonedTypeAdapterFactoryListsAreIndependent() {
+  @Test
+  void testClonedTypeAdapterFactoryListsAreIndependent() {
     Gson original = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
         true, true, false, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
@@ -86,7 +91,8 @@ private static final class TestTypeAdapter extends TypeAdapter<Object> {
     @Override public Object read(JsonReader in) throws IOException { return null; }
   }
 
-  public void testNewJsonWriter_Default() throws IOException {
+  @Test
+  void testNewJsonWriter_Default() throws IOException {
     StringWriter writer = new StringWriter();
     JsonWriter jsonWriter = new Gson().newJsonWriter(writer);
     jsonWriter.beginObject();
@@ -108,7 +114,8 @@ public void testNewJsonWriter_Default() throws IOException {
     assertEquals("{\"\\u003ctest2\":true}", writer.toString());
   }
 
-  public void testNewJsonWriter_Custom() throws IOException {
+  @Test
+  void testNewJsonWriter_Custom() throws IOException {
     StringWriter writer = new StringWriter();
     JsonWriter jsonWriter = new GsonBuilder()
       .disableHtmlEscaping()
@@ -132,7 +139,8 @@ public void testNewJsonWriter_Custom() throws IOException {
     assertEquals(")]}'\n{\n  \"test\": null,\n  \"<test2\": true\n}1", writer.toString());
   }
 
-  public void testNewJsonReader_Default() throws IOException {
+  @Test
+  void testNewJsonReader_Default() throws IOException {
     String json = "test"; // String without quotes
     JsonReader jsonReader = new Gson().newJsonReader(new StringReader(json));
     try {
@@ -143,7 +151,8 @@ public void testNewJsonReader_Default() throws IOException {
     jsonReader.close();
   }
 
-  public void testNewJsonReader_Custom() throws IOException {
+  @Test
+  void testNewJsonReader_Custom() throws IOException {
     String json = "test"; // String without quotes
     JsonReader jsonReader = new GsonBuilder()
       .setLenient()
diff --git a/gson/src/test/java/com/google/gson/GsonTypeAdapterTest.java b/gson/src/test/java/com/google/gson/GsonTypeAdapterTest.java
index decb93d83c..2f581dc92b 100644
--- a/gson/src/test/java/com/google/gson/GsonTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/GsonTypeAdapterTest.java
@@ -16,11 +16,15 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import java.lang.reflect.Type;
 import java.math.BigInteger;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Contains numerous tests involving registered type converters with a Gson instance.
@@ -28,26 +32,27 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class GsonTypeAdapterTest extends TestCase {
+class GsonTypeAdapterTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder()
         .registerTypeAdapter(AtomicLong.class, new ExceptionTypeAdapter())
         .registerTypeAdapter(AtomicInteger.class, new AtomicIntegerTypeAdapter())
         .create();
   }
 
-  public void testDefaultTypeAdapterThrowsParseException() throws Exception {
+  @Test
+  void testDefaultTypeAdapterThrowsParseException() throws Exception {
     try {
       gson.fromJson("{\"abc\":123}", BigInteger.class);
       fail("Should have thrown a JsonParseException");
     } catch (JsonParseException expected) { }
   }
 
-  public void testTypeAdapterThrowsException() throws Exception {
+  @Test
+  void testTypeAdapterThrowsException() throws Exception {
     try {
       gson.toJson(new AtomicLong(0));
       fail("Type Adapter should have thrown an exception");
@@ -59,7 +64,8 @@ public void testTypeAdapterThrowsException() throws Exception {
     } catch (JsonParseException expected) { }
   }
 
-  public void testTypeAdapterProperlyConvertsTypes() throws Exception {
+  @Test
+  void testTypeAdapterProperlyConvertsTypes() throws Exception {
     int intialValue = 1;
     AtomicInteger atomicInt = new AtomicInteger(intialValue);
     String json = gson.toJson(atomicInt);
@@ -69,7 +75,8 @@ public void testTypeAdapterProperlyConvertsTypes() throws Exception {
     assertEquals(intialValue, atomicInt.get());
   }
 
-  public void testTypeAdapterDoesNotAffectNonAdaptedTypes() throws Exception {
+  @Test
+  void testTypeAdapterDoesNotAffectNonAdaptedTypes() throws Exception {
     String expected = "blah";
     String actual = gson.toJson(expected);
     assertEquals("\"" + expected + "\"", actual);
@@ -82,12 +89,12 @@ private static class ExceptionTypeAdapter
       implements JsonSerializer<AtomicLong>, JsonDeserializer<AtomicLong> {
     @Override public JsonElement serialize(
         AtomicLong src, Type typeOfSrc, JsonSerializationContext context) {
-      throw new IllegalStateException();
+      throw new IllegalStateException("custom-exception");
     }
     @Override public AtomicLong deserialize(
         JsonElement json, Type typeOfT, JsonDeserializationContext context)
         throws JsonParseException {
-      throw new IllegalStateException();
+      throw new IllegalStateException("custom-exception");
     }
   }
 
@@ -113,7 +120,8 @@ static class Concrete extends Abstract {
   }
 
   // https://groups.google.com/d/topic/google-gson/EBmOCa8kJPE/discussion
-  public void testDeserializerForAbstractClass() {
+  @Test
+  void testDeserializerForAbstractClass() {
     Concrete instance = new Concrete();
     instance.a = "android";
     instance.b = "beep";
diff --git a/gson/src/test/java/com/google/gson/InnerClassExclusionStrategyTest.java b/gson/src/test/java/com/google/gson/InnerClassExclusionStrategyTest.java
index 86f7a62247..51f1f0c4ff 100644
--- a/gson/src/test/java/com/google/gson/InnerClassExclusionStrategyTest.java
+++ b/gson/src/test/java/com/google/gson/InnerClassExclusionStrategyTest.java
@@ -16,36 +16,43 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.internal.Excluder;
 import java.lang.reflect.Field;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for GsonBuilder.EXCLUDE_INNER_CLASSES.
  *
  * @author Joel Leitch
  */
-public class InnerClassExclusionStrategyTest extends TestCase {
+class InnerClassExclusionStrategyTest {
   public InnerClass innerClass = new InnerClass();
   public StaticNestedClass staticNestedClass = new StaticNestedClass();
-  private Excluder excluder = Excluder.DEFAULT.disableInnerClassSerialization();
+  public Excluder excluder = Excluder.DEFAULT.disableInnerClassSerialization();
 
-  public void testExcludeInnerClassObject() throws Exception {
+  @Test
+  void testExcludeInnerClassObject() throws Exception {
     Class<?> clazz = innerClass.getClass();
     assertTrue(excluder.excludeClass(clazz, true));
   }
 
-  public void testExcludeInnerClassField() throws Exception {
+  @Test
+  void testExcludeInnerClassField() throws Exception {
     Field f = getClass().getField("innerClass");
     assertTrue(excluder.excludeField(f, true));
   }
 
-  public void testIncludeStaticNestedClassObject() throws Exception {
+  @Test
+  void testIncludeStaticNestedClassObject() throws Exception {
     Class<?> clazz = staticNestedClass.getClass();
     assertFalse(excluder.excludeClass(clazz, true));
   }
 
-  public void testIncludeStaticNestedClassField() throws Exception {
+  @Test
+  void testIncludeStaticNestedClassField() throws Exception {
     Field f = getClass().getField("staticNestedClass");
     assertFalse(excluder.excludeField(f, true));
   }
diff --git a/gson/src/test/java/com/google/gson/JavaSerializationTest.java b/gson/src/test/java/com/google/gson/JavaSerializationTest.java
index fbaea19d43..ec1ca403ec 100644
--- a/gson/src/test/java/com/google/gson/JavaSerializationTest.java
+++ b/gson/src/test/java/com/google/gson/JavaSerializationTest.java
@@ -16,6 +16,8 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.reflect.TypeToken;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
@@ -27,17 +29,18 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Check that Gson doesn't return non-serializable data types.
  *
  * @author Jesse Wilson
  */
-public final class JavaSerializationTest extends TestCase {
+class JavaSerializationTest {
   private final Gson gson = new Gson();
 
-  public void testMapIsSerializable() throws Exception {
+  @Test
+  void testMapIsSerializable() throws Exception {
     Type type = new TypeToken<Map<String, Integer>>() {}.getType();
     Map<String, Integer> map = gson.fromJson("{\"b\":1,\"c\":2,\"a\":3}", type);
     Map<String, Integer> serialized = serializedCopy(map);
@@ -46,14 +49,16 @@ public void testMapIsSerializable() throws Exception {
     assertEquals(Arrays.asList("b", "c", "a"), new ArrayList<String>(serialized.keySet()));
   }
 
-  public void testListIsSerializable() throws Exception {
+  @Test
+  void testListIsSerializable() throws Exception {
     Type type = new TypeToken<List<String>>() {}.getType();
     List<String> list = gson.fromJson("[\"a\",\"b\",\"c\"]", type);
     List<String> serialized = serializedCopy(list);
     assertEquals(list, serialized);
   }
 
-  public void testNumberIsSerializable() throws Exception {
+  @Test
+  void testNumberIsSerializable() throws Exception {
     Type type = new TypeToken<List<Number>>() {}.getType();
     List<Number> list = gson.fromJson("[1,3.14,6.673e-11]", type);
     List<Number> serialized = serializedCopy(list);
diff --git a/gson/src/test/java/com/google/gson/JsonArrayTest.java b/gson/src/test/java/com/google/gson/JsonArrayTest.java
index 3975ce2c84..072e7dc01c 100644
--- a/gson/src/test/java/com/google/gson/JsonArrayTest.java
+++ b/gson/src/test/java/com/google/gson/JsonArrayTest.java
@@ -16,19 +16,26 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.common.MoreAsserts;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * @author Jesse Wilson
  */
-public final class JsonArrayTest extends TestCase {
-
-  public void testEqualsOnEmptyArray() {
+class JsonArrayTest {
+  @Test
+  void testEqualsOnEmptyArray() {
     MoreAsserts.assertEqualsAndHashCode(new JsonArray(), new JsonArray());
   }
 
-  public void testEqualsNonEmptyArray() {
+  @Test
+  void testEqualsNonEmptyArray() {
     JsonArray a = new JsonArray();
     JsonArray b = new JsonArray();
 
@@ -50,7 +57,8 @@ public void testEqualsNonEmptyArray() {
     assertFalse(b.equals(a));
   }
 
-  public void testRemove() {
+  @Test
+  void testRemove() {
     JsonArray array = new JsonArray();
     try {
       array.remove(0);
@@ -67,7 +75,8 @@ public void testRemove() {
     assertTrue(array.contains(a));
   }
 
-  public void testSet() {
+  @Test
+  void testSet() {
     JsonArray array = new JsonArray();
     try {
       array.set(0, new JsonPrimitive(1));
@@ -84,7 +93,8 @@ public void testSet() {
     assertEquals(1, array.size());
   }
 
-  public void testDeepCopy() {
+  @Test
+  void testDeepCopy() {
     JsonArray original = new JsonArray();
     JsonArray firstEntry = new JsonArray();
     original.add(firstEntry);
@@ -99,29 +109,27 @@ public void testDeepCopy() {
     assertEquals(0, copy.get(0).getAsJsonArray().size());
   }
 
-  public void testFailedGetArrayValues() {
+  @Test
+  void testFailedGetArrayValues() {
     JsonArray jsonArray = new JsonArray();
     jsonArray.add(JsonParser.parseString("{" + "\"key1\":\"value1\"," + "\"key2\":\"value2\"," + "\"key3\":\"value3\"," + "\"key4\":\"value4\"" + "}"));
     try {
       jsonArray.getAsBoolean();
       fail("expected getBoolean to fail");
     } catch (UnsupportedOperationException e) {
-      assertEquals("Expected an exception message",
-              "JsonObject", e.getMessage());
+      assertEquals("JsonObject", e.getMessage());
     }
     try {
       jsonArray.get(-1);
       fail("expected get to fail");
     } catch (IndexOutOfBoundsException e) {
-      assertEquals("Expected an exception message",
-              "Index -1 out of bounds for length 1", e.getMessage());
+      assertEquals("Index -1 out of bounds for length 1", e.getMessage());
     }
     try {
       jsonArray.getAsString();
       fail("expected getString to fail");
     } catch (UnsupportedOperationException e) {
-      assertEquals("Expected an exception message",
-              "JsonObject", e.getMessage());
+      assertEquals("JsonObject", e.getMessage());
     }
 
     jsonArray.remove(0);
@@ -130,36 +138,31 @@ public void testFailedGetArrayValues() {
       jsonArray.getAsDouble();
       fail("expected getDouble to fail");
     } catch (NumberFormatException e) {
-      assertEquals("Expected an exception message",
-              "For input string: \"hello\"", e.getMessage());
+      assertEquals("For input string: \"hello\"", e.getMessage());
     }
     try {
       jsonArray.getAsInt();
       fail("expected getInt to fail");
     } catch (NumberFormatException e) {
-      assertEquals("Expected an exception message",
-              "For input string: \"hello\"", e.getMessage());
+      assertEquals("For input string: \"hello\"", e.getMessage());
     }
     try {
       jsonArray.get(0).getAsJsonArray();
       fail("expected getJSONArray to fail");
     } catch (IllegalStateException e) {
-      assertEquals("Expected an exception message",
-              "Not a JSON Array: \"hello\"", e.getMessage());
+      assertEquals("Not a JSON Array: \"hello\"", e.getMessage());
     }
     try {
       jsonArray.getAsJsonObject();
       fail("expected getJSONObject to fail");
     } catch (IllegalStateException e) {
-      assertEquals("Expected an exception message",
-              "Not a JSON Object: [\"hello\"]", e.getMessage());
+      assertEquals("Not a JSON Object: [\"hello\"]", e.getMessage());
     }
     try {
       jsonArray.getAsLong();
       fail("expected getLong to fail");
     } catch (NumberFormatException e) {
-      assertEquals("Expected an exception message",
-              "For input string: \"hello\"", e.getMessage());
+      assertEquals("For input string: \"hello\"", e.getMessage());
     }
   }
 }
diff --git a/gson/src/test/java/com/google/gson/JsonNullTest.java b/gson/src/test/java/com/google/gson/JsonNullTest.java
index 6157e38765..3e035b884d 100644
--- a/gson/src/test/java/com/google/gson/JsonNullTest.java
+++ b/gson/src/test/java/com/google/gson/JsonNullTest.java
@@ -16,22 +16,26 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertSame;
+
 import com.google.gson.common.MoreAsserts;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * @author Jesse Wilson
  */
-public final class JsonNullTest extends TestCase {
+class JsonNullTest {
 
   @SuppressWarnings("deprecation")
-  public void testEqualsAndHashcode() {
+  @Test
+  void testEqualsAndHashcode() {
     MoreAsserts.assertEqualsAndHashCode(new JsonNull(), new JsonNull());
     MoreAsserts.assertEqualsAndHashCode(new JsonNull(), JsonNull.INSTANCE);
     MoreAsserts.assertEqualsAndHashCode(JsonNull.INSTANCE, JsonNull.INSTANCE);
   }
 
-  public void testDeepCopy() {
+  @Test
+  void testDeepCopy() {
     @SuppressWarnings("deprecation")
     JsonNull a = new JsonNull();
     assertSame(JsonNull.INSTANCE, a.deepCopy());
diff --git a/gson/src/test/java/com/google/gson/JsonObjectTest.java b/gson/src/test/java/com/google/gson/JsonObjectTest.java
index 6f5274fcc8..04888ba752 100644
--- a/gson/src/test/java/com/google/gson/JsonObjectTest.java
+++ b/gson/src/test/java/com/google/gson/JsonObjectTest.java
@@ -16,18 +16,25 @@
 
 package com.google.gson;
 
-import com.google.gson.common.MoreAsserts;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
-import junit.framework.TestCase;
+import com.google.gson.common.MoreAsserts;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for the {@link JsonObject} class.
  *
  * @author Joel Leitch
  */
-public class JsonObjectTest extends TestCase {
+class JsonObjectTest {
 
-  public void testAddingAndRemovingObjectProperties() throws Exception {
+  @Test
+  void testAddingAndRemovingObjectProperties() throws Exception {
     JsonObject jsonObj = new JsonObject();
     String propertyName = "property";
     assertFalse(jsonObj.has(propertyName));
@@ -43,7 +50,8 @@ public void testAddingAndRemovingObjectProperties() throws Exception {
     assertNull(jsonObj.get(propertyName));
   }
 
-  public void testAddingNullPropertyValue() throws Exception {
+  @Test
+  void testAddingNullPropertyValue() throws Exception {
     String propertyName = "property";
     JsonObject jsonObj = new JsonObject();
     jsonObj.add(propertyName, null);
@@ -55,7 +63,8 @@ public void testAddingNullPropertyValue() throws Exception {
     assertTrue(jsonElement.isJsonNull());
   }
 
-  public void testAddingNullOrEmptyPropertyName() throws Exception {
+  @Test
+  void testAddingNullOrEmptyPropertyName() throws Exception {
     JsonObject jsonObj = new JsonObject();
     try {
       jsonObj.add(null, JsonNull.INSTANCE);
@@ -66,7 +75,8 @@ public void testAddingNullOrEmptyPropertyName() throws Exception {
     jsonObj.add("   \t", JsonNull.INSTANCE);
   }
 
-  public void testAddingBooleanProperties() throws Exception {
+  @Test
+  void testAddingBooleanProperties() throws Exception {
     String propertyName = "property";
     JsonObject jsonObj = new JsonObject();
     jsonObj.addProperty(propertyName, true);
@@ -78,7 +88,8 @@ public void testAddingBooleanProperties() throws Exception {
     assertTrue(jsonElement.getAsBoolean());
   }
 
-  public void testAddingStringProperties() throws Exception {
+  @Test
+  void testAddingStringProperties() throws Exception {
     String propertyName = "property";
     String value = "blah";
 
@@ -92,7 +103,8 @@ public void testAddingStringProperties() throws Exception {
     assertEquals(value, jsonElement.getAsString());
   }
 
-  public void testAddingCharacterProperties() throws Exception {
+  @Test
+  void testAddingCharacterProperties() throws Exception {
     String propertyName = "property";
     char value = 'a';
 
@@ -113,7 +125,8 @@ public void testAddingCharacterProperties() throws Exception {
   /**
    * From bug report http://code.google.com/p/google-gson/issues/detail?id=182
    */
-  public void testPropertyWithQuotes() {
+  @Test
+  void testPropertyWithQuotes() {
     JsonObject jsonObj = new JsonObject();
     jsonObj.add("a\"b", new JsonPrimitive("c\"d"));
     String json = new Gson().toJson(jsonObj);
@@ -123,27 +136,30 @@ public void testPropertyWithQuotes() {
   /**
    * From issue 227.
    */
-  public void testWritePropertyWithEmptyStringName() {
+  @Test
+  void testWritePropertyWithEmptyStringName() {
     JsonObject jsonObj = new JsonObject();
     jsonObj.add("", new JsonPrimitive(true));
     assertEquals("{\"\":true}", new Gson().toJson(jsonObj));
-
   }
 
-  public void testReadPropertyWithEmptyStringName() {
+  @Test
+  void testReadPropertyWithEmptyStringName() {
     JsonObject jsonObj = JsonParser.parseString("{\"\":true}").getAsJsonObject();
     assertEquals(true, jsonObj.get("").getAsBoolean());
   }
 
-  public void testEqualsOnEmptyObject() {
+  @Test
+  void testEqualsOnEmptyObject() {
     MoreAsserts.assertEqualsAndHashCode(new JsonObject(), new JsonObject());
   }
 
-  public void testEqualsNonEmptyObject() {
+  @Test
+  void testEqualsNonEmptyObject() {
     JsonObject a = new JsonObject();
     JsonObject b = new JsonObject();
 
-    assertEquals(a, a);
+    assertTrue(a.equals(a));
 
     a.add("foo", new JsonObject());
     assertFalse(a.equals(b));
@@ -161,7 +177,8 @@ public void testEqualsNonEmptyObject() {
     assertFalse(b.equals(a));
   }
 
-  public void testSize() {
+  @Test
+  void testSize() {
     JsonObject o = new JsonObject();
     assertEquals(0, o.size());
 
@@ -175,7 +192,8 @@ public void testSize() {
     assertEquals(1, o.size());
   }
 
-  public void testDeepCopy() {
+  @Test
+  void testDeepCopy() {
     JsonObject original = new JsonObject();
     JsonArray firstEntry = new JsonArray();
     original.add("key", firstEntry);
@@ -190,7 +208,8 @@ public void testDeepCopy() {
   /**
    * From issue 941
    */
-  public void testKeySet() {
+  @Test
+  void testKeySet() {
     JsonObject a = new JsonObject();
 
     a.add("foo", new JsonArray());
diff --git a/gson/src/test/java/com/google/gson/JsonParserTest.java b/gson/src/test/java/com/google/gson/JsonParserTest.java
index cc18238be4..8d70031fdd 100644
--- a/gson/src/test/java/com/google/gson/JsonParserTest.java
+++ b/gson/src/test/java/com/google/gson/JsonParserTest.java
@@ -16,31 +16,35 @@
 
 package com.google.gson;
 
-import java.io.CharArrayReader;
-import java.io.CharArrayWriter;
-import java.io.StringReader;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.internal.Streams;
 import com.google.gson.stream.JsonReader;
+import java.io.CharArrayReader;
+import java.io.CharArrayWriter;
+import java.io.StringReader;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for {@link JsonParser}
  *
  * @author Inderjeet Singh
  */
-public class JsonParserTest extends TestCase {
+class JsonParserTest {
 
-  public void testParseInvalidJson() {
+  @Test
+  void testParseInvalidJson() {
     try {
       JsonParser.parseString("[[]");
       fail();
     } catch (JsonSyntaxException expected) { }
   }
 
-  public void testParseUnquotedStringArrayFails() {
+  @Test
+  void testParseUnquotedStringArrayFails() {
     JsonElement element = JsonParser.parseString("[a,b,c]");
     assertEquals("a", element.getAsJsonArray().get(0).getAsString());
     assertEquals("b", element.getAsJsonArray().get(1).getAsString());
@@ -48,7 +52,8 @@ public void testParseUnquotedStringArrayFails() {
     assertEquals(3, element.getAsJsonArray().size());
   }
 
-  public void testParseString() {
+  @Test
+  void testParseString() {
     String json = "{a:10,b:'c'}";
     JsonElement e = JsonParser.parseString(json);
     assertTrue(e.isJsonObject());
@@ -56,22 +61,26 @@ public void testParseString() {
     assertEquals("c", e.getAsJsonObject().get("b").getAsString());
   }
 
-  public void testParseEmptyString() {
+  @Test
+  void testParseEmptyString() {
     JsonElement e = JsonParser.parseString("\"   \"");
     assertTrue(e.isJsonPrimitive());
     assertEquals("   ", e.getAsString());
   }
 
-  public void testParseEmptyWhitespaceInput() {
+  @Test
+  void testParseEmptyWhitespaceInput() {
     JsonElement e = JsonParser.parseString("     ");
     assertTrue(e.isJsonNull());
   }
 
-  public void testParseUnquotedSingleWordStringFails() {
+  @Test
+  void testParseUnquotedSingleWordStringFails() {
     assertEquals("Test", JsonParser.parseString("Test").getAsString());
   }
 
-  public void testParseUnquotedMultiWordStringFails() {
+  @Test
+  void testParseUnquotedMultiWordStringFails() {
     String unquotedSentence = "Test is a test..blah blah";
     try {
       JsonParser.parseString(unquotedSentence);
@@ -79,7 +88,8 @@ public void testParseUnquotedMultiWordStringFails() {
     } catch (JsonSyntaxException expected) { }
   }
 
-  public void testParseMixedArray() {
+  @Test
+  void testParseMixedArray() {
     String json = "[{},13,\"stringValue\"]";
     JsonElement e = JsonParser.parseString(json);
     assertTrue(e.isJsonArray());
@@ -90,7 +100,8 @@ public void testParseMixedArray() {
     assertEquals("stringValue", array.get(2).getAsString());
   }
 
-  public void testParseReader() {
+  @Test
+  void testParseReader() {
     StringReader reader = new StringReader("{a:10,b:'c'}");
     JsonElement e = JsonParser.parseReader(reader);
     assertTrue(e.isJsonObject());
@@ -98,7 +109,8 @@ public void testParseReader() {
     assertEquals("c", e.getAsJsonObject().get("b").getAsString());
   }
 
-  public void testReadWriteTwoObjects() throws Exception {
+  @Test
+  void testReadWriteTwoObjects() throws Exception {
     Gson gson = new Gson();
     CharArrayWriter writer = new CharArrayWriter();
     BagOfPrimitives expectedOne = new BagOfPrimitives(1, 1, true, "one");
diff --git a/gson/src/test/java/com/google/gson/JsonPrimitiveTest.java b/gson/src/test/java/com/google/gson/JsonPrimitiveTest.java
index cdd4fdb613..7f0a39f0d5 100644
--- a/gson/src/test/java/com/google/gson/JsonPrimitiveTest.java
+++ b/gson/src/test/java/com/google/gson/JsonPrimitiveTest.java
@@ -16,22 +16,26 @@
 
 package com.google.gson;
 
-import com.google.gson.common.MoreAsserts;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
+import com.google.gson.common.MoreAsserts;
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for the {@link JsonPrimitive} class.
  *
  * @author Joel Leitch
  */
-public class JsonPrimitiveTest extends TestCase {
+ class JsonPrimitiveTest {
 
-  @SuppressWarnings("unused")
-  public void testNulls() {
+  @Test
+  void testNulls() {
     try {
       new JsonPrimitive((Boolean) null);
       fail();
@@ -54,7 +58,8 @@ public void testNulls() {
     }
   }
 
-  public void testBoolean() throws Exception {
+  @Test
+  void testBoolean() throws Exception {
     JsonPrimitive json = new JsonPrimitive(Boolean.TRUE);
 
     assertTrue(json.isBoolean());
@@ -77,14 +82,16 @@ public void testBoolean() throws Exception {
     assertFalse(json.getAsBoolean());
   }
 
-  public void testParsingStringAsBoolean() throws Exception {
+  @Test
+  void testParsingStringAsBoolean() throws Exception {
     JsonPrimitive json = new JsonPrimitive("true");
 
     assertFalse(json.isBoolean());
     assertTrue(json.getAsBoolean());
   }
 
-  public void testParsingStringAsNumber() throws Exception {
+  @Test
+  void testParsingStringAsNumber() throws Exception {
     JsonPrimitive json = new JsonPrimitive("1");
 
     assertFalse(json.isNumber());
@@ -98,7 +105,8 @@ public void testParsingStringAsNumber() throws Exception {
     assertEquals(new BigDecimal("1"), json.getAsBigDecimal());
   }
 
-  public void testStringsAndChar() throws Exception {
+  @Test
+  void testStringsAndChar() throws Exception {
     JsonPrimitive json = new JsonPrimitive("abc");
     assertTrue(json.isString());
     assertEquals('a', json.getAsCharacter());
@@ -113,7 +121,8 @@ public void testStringsAndChar() throws Exception {
     assertEquals("true", json.getAsString());
   }
 
-  public void testExponential() throws Exception {
+  @Test
+  void testExponential() throws Exception {
     JsonPrimitive json = new JsonPrimitive("1E+7");
 
     assertEquals(new BigDecimal("1E+7"), json.getAsBigDecimal());
@@ -126,98 +135,99 @@ public void testExponential() throws Exception {
     } catch (NumberFormatException expected) { }
   }
 
-  public void testByteEqualsShort() {
+  @Test
+  void testByteEqualsShort() {
     JsonPrimitive p1 = new JsonPrimitive(Byte.valueOf((byte)10));
     JsonPrimitive p2 = new JsonPrimitive(Short.valueOf((short)10));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testByteEqualsInteger() {
+  @Test
+  void testByteEqualsInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Byte.valueOf((byte)10));
     JsonPrimitive p2 = new JsonPrimitive(Integer.valueOf(10));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testByteEqualsLong() {
+  @Test
+  void testByteEqualsLong() {
     JsonPrimitive p1 = new JsonPrimitive(Byte.valueOf((byte)10));
     JsonPrimitive p2 = new JsonPrimitive(Long.valueOf(10L));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testByteEqualsBigInteger() {
+  @Test
+  void testByteEqualsBigInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Byte.valueOf((byte)10));
     JsonPrimitive p2 = new JsonPrimitive(new BigInteger("10"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testShortEqualsInteger() {
+  @Test
+  void testShortEqualsInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Short.valueOf((short)10));
     JsonPrimitive p2 = new JsonPrimitive(Integer.valueOf(10));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testShortEqualsLong() {
+  @Test
+  void testShortEqualsLong() {
     JsonPrimitive p1 = new JsonPrimitive(Short.valueOf((short)10));
     JsonPrimitive p2 = new JsonPrimitive(Long.valueOf(10));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testShortEqualsBigInteger() {
+  @Test
+  void testShortEqualsBigInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Short.valueOf((short)10));
     JsonPrimitive p2 = new JsonPrimitive(new BigInteger("10"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testIntegerEqualsLong() {
+  @Test
+  void testIntegerEqualsLong() {
     JsonPrimitive p1 = new JsonPrimitive(Integer.valueOf(10));
     JsonPrimitive p2 = new JsonPrimitive(Long.valueOf(10L));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testIntegerEqualsBigInteger() {
+  @Test
+  void testIntegerEqualsBigInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Integer.valueOf(10));
     JsonPrimitive p2 = new JsonPrimitive(new BigInteger("10"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testLongEqualsBigInteger() {
+  @Test
+  void testLongEqualsBigInteger() {
     JsonPrimitive p1 = new JsonPrimitive(Long.valueOf(10L));
     JsonPrimitive p2 = new JsonPrimitive(new BigInteger("10"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testFloatEqualsDouble() {
+  @Test
+  void testFloatEqualsDouble() {
     JsonPrimitive p1 = new JsonPrimitive(Float.valueOf(10.25F));
     JsonPrimitive p2 = new JsonPrimitive(Double.valueOf(10.25D));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testFloatEqualsBigDecimal() {
+  @Test
+  void testFloatEqualsBigDecimal() {
     JsonPrimitive p1 = new JsonPrimitive(Float.valueOf(10.25F));
     JsonPrimitive p2 = new JsonPrimitive(new BigDecimal("10.25"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testDoubleEqualsBigDecimal() {
+  @Test
+  void testDoubleEqualsBigDecimal() {
     JsonPrimitive p1 = new JsonPrimitive(Double.valueOf(10.25D));
     JsonPrimitive p2 = new JsonPrimitive(new BigDecimal("10.25"));
-    assertEquals(p1, p2);
-    assertEquals(p1.hashCode(), p2.hashCode());
+    MoreAsserts.assertEqualsAndHashCode(p1, p2);
   }
 
-  public void testValidJsonOnToString() throws Exception {
+  @Test
+  void testValidJsonOnToString() throws Exception {
     JsonPrimitive json = new JsonPrimitive("Some\nEscaped\nValue");
     assertEquals("\"Some\\nEscaped\\nValue\"", json.toString());
 
@@ -225,7 +235,8 @@ public void testValidJsonOnToString() throws Exception {
     assertEquals("1.333", json.toString());
   }
 
-  public void testEquals() {
+  @Test
+  void testEquals() {
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive("A"), new JsonPrimitive("A"));
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive(true), new JsonPrimitive(true));
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive(5L), new JsonPrimitive(5L));
@@ -245,7 +256,8 @@ public void testEquals() {
     assertFalse(new JsonPrimitive(0).equals(new JsonPrimitive(1)));
   }
 
-  public void testEqualsAcrossTypes() {
+  @Test
+  void testEqualsAcrossTypes() {
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive("a"), new JsonPrimitive('a'));
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive(new BigInteger("0")), new JsonPrimitive(0));
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive(0), new JsonPrimitive(0L));
@@ -253,21 +265,24 @@ public void testEqualsAcrossTypes() {
     MoreAsserts.assertEqualsAndHashCode(new JsonPrimitive(Float.NaN), new JsonPrimitive(Double.NaN));
   }
 
-  public void testEqualsIntegerAndBigInteger() {
+  @Test
+  void testEqualsIntegerAndBigInteger() {
     JsonPrimitive a = new JsonPrimitive(5L);
     JsonPrimitive b = new JsonPrimitive(new BigInteger("18446744073709551621")); // 2^64 + 5
     // Ideally, the following assertion should have failed but the price is too much to pay 
     // assertFalse(a + " equals " + b, a.equals(b));
-    assertTrue(a + " equals " + b, a.equals(b));
+    assertTrue(a.equals(b), a + " equals " + b);
   }
 
-  public void testEqualsDoesNotEquateStringAndNonStringTypes() {
+  @Test
+  void testEqualsDoesNotEquateStringAndNonStringTypes() {
     assertFalse(new JsonPrimitive("true").equals(new JsonPrimitive(true)));
     assertFalse(new JsonPrimitive("0").equals(new JsonPrimitive(0)));
     assertFalse(new JsonPrimitive("NaN").equals(new JsonPrimitive(Float.NaN)));
   }
 
-  public void testDeepCopy() {
+  @Test
+  void testDeepCopy() {
     JsonPrimitive a = new JsonPrimitive("a");
     assertSame(a, a.deepCopy()); // Primitives are immutable!
   }
diff --git a/gson/src/test/java/com/google/gson/JsonStreamParserTest.java b/gson/src/test/java/com/google/gson/JsonStreamParserTest.java
index 1b40b58b6f..604a43ec9d 100644
--- a/gson/src/test/java/com/google/gson/JsonStreamParserTest.java
+++ b/gson/src/test/java/com/google/gson/JsonStreamParserTest.java
@@ -15,32 +15,38 @@
  */
 package com.google.gson;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import java.util.NoSuchElementException;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for {@link JsonStreamParser}
  * 
  * @author Inderjeet Singh
  */
-public class JsonStreamParserTest extends TestCase {
+class JsonStreamParserTest {
   private JsonStreamParser parser;
   
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     parser = new JsonStreamParser("'one' 'two'");
   }
 
-  public void testParseTwoStrings() {
+  @Test
+  void testParseTwoStrings() {
     String actualOne = parser.next().getAsString();
     assertEquals("one", actualOne);
     String actualTwo = parser.next().getAsString();
     assertEquals("two", actualTwo);
   }
 
-  public void testIterator() {
+  @Test
+  void testIterator() {
     assertTrue(parser.hasNext());
     assertEquals("one", parser.next().getAsString());
     assertTrue(parser.hasNext());
@@ -48,7 +54,8 @@ public void testIterator() {
     assertFalse(parser.hasNext());
   }
 
-  public void testNoSideEffectForHasNext() throws Exception {
+  @Test
+  void testNoSideEffectForHasNext() throws Exception {
     assertTrue(parser.hasNext());
     assertTrue(parser.hasNext());
     assertTrue(parser.hasNext());
@@ -62,7 +69,8 @@ public void testNoSideEffectForHasNext() throws Exception {
     assertFalse(parser.hasNext());
   }
 
-  public void testCallingNextBeyondAvailableInput() {
+  @Test
+  void testCallingNextBeyondAvailableInput() {
     parser.next();
     parser.next();
     try {
diff --git a/gson/src/test/java/com/google/gson/LongSerializationPolicyTest.java b/gson/src/test/java/com/google/gson/LongSerializationPolicyTest.java
index a4ad8f1423..34fb51445d 100644
--- a/gson/src/test/java/com/google/gson/LongSerializationPolicyTest.java
+++ b/gson/src/test/java/com/google/gson/LongSerializationPolicyTest.java
@@ -16,7 +16,11 @@
 
 package com.google.gson;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit test for the {@link LongSerializationPolicy} class.
@@ -24,9 +28,10 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class LongSerializationPolicyTest extends TestCase {
+class LongSerializationPolicyTest {
 
-  public void testDefaultLongSerialization() throws Exception {
+  @Test
+  void testDefaultLongSerialization() throws Exception {
     JsonElement element = LongSerializationPolicy.DEFAULT.serialize(1556L);
     assertTrue(element.isJsonPrimitive());
 
@@ -36,7 +41,8 @@ public void testDefaultLongSerialization() throws Exception {
     assertEquals(1556L, element.getAsLong());
   }
 
-  public void testDefaultLongSerializationIntegration() {
+  @Test
+  void testDefaultLongSerializationIntegration() {
     Gson gson = new GsonBuilder()
       .setLongSerializationPolicy(LongSerializationPolicy.DEFAULT)
       .create();
@@ -44,7 +50,8 @@ public void testDefaultLongSerializationIntegration() {
     assertEquals("[1]", gson.toJson(new Long[] { 1L }, Long[].class));
   }
 
-  public void testDefaultLongSerializationNull() {
+  @Test
+  void testDefaultLongSerializationNull() {
     LongSerializationPolicy policy = LongSerializationPolicy.DEFAULT;
     assertTrue(policy.serialize(null).isJsonNull());
 
@@ -54,7 +61,8 @@ public void testDefaultLongSerializationNull() {
     assertEquals("null", gson.toJson(null, Long.class));
   }
 
-  public void testStringLongSerialization() throws Exception {
+  @Test
+  void testStringLongSerialization() throws Exception {
     JsonElement element = LongSerializationPolicy.STRING.serialize(1556L);
     assertTrue(element.isJsonPrimitive());
 
@@ -64,7 +72,8 @@ public void testStringLongSerialization() throws Exception {
     assertEquals("1556", element.getAsString());
   }
 
-  public void testStringLongSerializationIntegration() {
+  @Test
+  void testStringLongSerializationIntegration() {
     Gson gson = new GsonBuilder()
       .setLongSerializationPolicy(LongSerializationPolicy.STRING)
       .create();
@@ -72,7 +81,8 @@ public void testStringLongSerializationIntegration() {
     assertEquals("[\"1\"]", gson.toJson(new Long[] { 1L }, Long[].class));
   }
 
-  public void testStringLongSerializationNull() {
+  @Test
+  void testStringLongSerializationNull() {
     LongSerializationPolicy policy = LongSerializationPolicy.STRING;
     assertTrue(policy.serialize(null).isJsonNull());
 
diff --git a/gson/src/test/java/com/google/gson/MixedStreamTest.java b/gson/src/test/java/com/google/gson/MixedStreamTest.java
index 00eb4bc8a0..3ddca8711c 100644
--- a/gson/src/test/java/com/google/gson/MixedStreamTest.java
+++ b/gson/src/test/java/com/google/gson/MixedStreamTest.java
@@ -16,6 +16,11 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
@@ -25,9 +30,9 @@
 import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.List;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class MixedStreamTest extends TestCase {
+class MixedStreamTest {
 
   private static final Car BLUE_MUSTANG = new Car("mustang", 0x0000FF);
   private static final Car BLACK_BMW = new Car("bmw", 0x000000);
@@ -47,7 +52,8 @@ public final class MixedStreamTest extends TestCase {
       + "  }\n"
       + "]";
 
-  public void testWriteMixedStreamed() throws IOException {
+  @Test
+  void testWriteMixedStreamed() throws IOException {
     Gson gson = new Gson();
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
@@ -62,7 +68,8 @@ public void testWriteMixedStreamed() throws IOException {
     assertEquals(CARS_JSON, stringWriter.toString());
   }
 
-  public void testReadMixedStreamed() throws IOException {
+  @Test
+  void testReadMixedStreamed() throws IOException {
     Gson gson = new Gson();
     StringReader stringReader = new StringReader(CARS_JSON);
     JsonReader jsonReader = new JsonReader(stringReader);
@@ -74,7 +81,8 @@ public void testReadMixedStreamed() throws IOException {
     jsonReader.endArray();
   }
 
-  public void testReaderDoesNotMutateState() throws IOException {
+  @Test
+  void testReaderDoesNotMutateState() throws IOException {
     Gson gson = new Gson();
     JsonReader jsonReader = new JsonReader(new StringReader(CARS_JSON));
     jsonReader.beginArray();
@@ -88,7 +96,8 @@ public void testReaderDoesNotMutateState() throws IOException {
     assertTrue(jsonReader.isLenient());
   }
 
-  public void testWriteDoesNotMutateState() throws IOException {
+  @Test
+  void testWriteDoesNotMutateState() throws IOException {
     Gson gson = new Gson();
     JsonWriter jsonWriter = new JsonWriter(new StringWriter());
     jsonWriter.beginArray();
@@ -106,7 +115,8 @@ public void testWriteDoesNotMutateState() throws IOException {
     assertFalse(jsonWriter.isLenient());
   }
 
-  public void testReadInvalidState() throws IOException {
+  @Test
+  void testReadInvalidState() throws IOException {
     Gson gson = new Gson();
     JsonReader jsonReader = new JsonReader(new StringReader(CARS_JSON));
     jsonReader.beginArray();
@@ -118,7 +128,8 @@ public void testReadInvalidState() throws IOException {
     }
   }
 
-  public void testReadClosed() throws IOException {
+  @Test
+  void testReadClosed() throws IOException {
     Gson gson = new Gson();
     JsonReader jsonReader = new JsonReader(new StringReader(CARS_JSON));
     jsonReader.close();
@@ -129,7 +140,8 @@ public void testReadClosed() throws IOException {
     }
   }
 
-  public void testWriteInvalidState() throws IOException {
+  @Test
+  void testWriteInvalidState() throws IOException {
     Gson gson = new Gson();
     JsonWriter jsonWriter = new JsonWriter(new StringWriter());
     jsonWriter.beginObject();
@@ -140,7 +152,8 @@ public void testWriteInvalidState() throws IOException {
     }
   }
 
-  public void testWriteClosed() throws IOException {
+  @Test
+  void testWriteClosed() throws IOException {
     Gson gson = new Gson();
     JsonWriter jsonWriter = new JsonWriter(new StringWriter());
     jsonWriter.beginArray();
@@ -153,7 +166,8 @@ public void testWriteClosed() throws IOException {
     }
   }
 
-  public void testWriteNulls() {
+  @Test
+  void testWriteNulls() {
     Gson gson = new Gson();
     try {
       gson.toJson(new JsonPrimitive("hello"), (JsonWriter) null);
@@ -166,7 +180,8 @@ public void testWriteNulls() {
     assertEquals("null", stringWriter.toString());
   }
 
-  public void testReadNulls() {
+  @Test
+  void testReadNulls() {
     Gson gson = new Gson();
     try {
       gson.fromJson((JsonReader) null, Integer.class);
@@ -180,7 +195,8 @@ public void testReadNulls() {
     }
   }
 
-  public void testWriteHtmlSafe() {
+  @Test
+  void testWriteHtmlSafe() {
     List<String> contents = Arrays.asList("<", ">", "&", "=", "'");
     Type type = new TypeToken<List<String>>() {}.getType();
 
@@ -196,7 +212,8 @@ public void testWriteHtmlSafe() {
         writer.toString());
   }
 
-  public void testWriteLenient() {
+  @Test
+  void testWriteLenient() {
     List<Double> doubles = Arrays.asList(Double.NaN, Double.NEGATIVE_INFINITY,
         Double.POSITIVE_INFINITY, -0.0d, 0.5d, 0.0d);
     Type type = new TypeToken<List<Double>>() {}.getType();
diff --git a/gson/src/test/java/com/google/gson/ObjectTypeAdapterTest.java b/gson/src/test/java/com/google/gson/ObjectTypeAdapterTest.java
index 2891bffca0..a43f648e8d 100644
--- a/gson/src/test/java/com/google/gson/ObjectTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/ObjectTypeAdapterTest.java
@@ -16,17 +16,20 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class ObjectTypeAdapterTest extends TestCase {
+class ObjectTypeAdapterTest {
   private final Gson gson = new GsonBuilder().create();
   private final TypeAdapter<Object> adapter = gson.getAdapter(Object.class);
 
-  public void testDeserialize() throws Exception {
+  @Test
+  void testDeserialize() throws Exception {
     Map<?, ?> map = (Map<?, ?>) adapter.fromJson("{\"a\":5,\"b\":[1,2,null],\"c\":{\"x\":\"y\"}}");
     assertEquals(5.0, map.get("a"));
     assertEquals(Arrays.asList(1.0, 2.0, null), map.get("b"));
@@ -34,24 +37,28 @@ public void testDeserialize() throws Exception {
     assertEquals(3, map.size());
   }
 
-  public void testSerialize() throws Exception {
+  @Test
+  void testSerialize() throws Exception {
     Object object = new RuntimeType();
     assertEquals("{'a':5,'b':[1,2,null]}", adapter.toJson(object).replace("\"", "'"));
   }
   
-  public void testSerializeNullValue() throws Exception {
+  @Test
+  void testSerializeNullValue() throws Exception {
     Map<String, Object> map = new LinkedHashMap<String, Object>();
     map.put("a", null);
     assertEquals("{'a':null}", adapter.toJson(map).replace('"', '\''));
   }
 
-  public void testDeserializeNullValue() throws Exception {
+  @Test
+  void testDeserializeNullValue() throws Exception {
     Map<String, Object> map = new LinkedHashMap<String, Object>();
     map.put("a", null);
     assertEquals(map, adapter.fromJson("{\"a\":null}"));
   }
 
-  public void testSerializeObject() throws Exception {
+  @Test
+  void testSerializeObject() throws Exception {
     assertEquals("{}", adapter.toJson(new Object()));
   }
 
diff --git a/gson/src/test/java/com/google/gson/OverrideCoreTypeAdaptersTest.java b/gson/src/test/java/com/google/gson/OverrideCoreTypeAdaptersTest.java
index 79ae1698f9..2bea2660b4 100644
--- a/gson/src/test/java/com/google/gson/OverrideCoreTypeAdaptersTest.java
+++ b/gson/src/test/java/com/google/gson/OverrideCoreTypeAdaptersTest.java
@@ -16,16 +16,18 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
 import java.util.Locale;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * @author Jesse Wilson
  */
-public class OverrideCoreTypeAdaptersTest extends TestCase {
+class OverrideCoreTypeAdaptersTest {
   private static final TypeAdapter<Boolean> booleanAsIntAdapter = new TypeAdapter<Boolean>() {
     @Override public void write(JsonWriter out, Boolean value) throws IOException {
       out.value(value ? 1 : 0);
@@ -45,7 +47,8 @@ public class OverrideCoreTypeAdaptersTest extends TestCase {
     }
   };
 
-  public void testOverrideWrapperBooleanAdapter() {
+  @Test
+  void testOverrideWrapperBooleanAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Boolean.class, booleanAsIntAdapter)
         .create();
@@ -56,7 +59,8 @@ public void testOverrideWrapperBooleanAdapter() {
     assertEquals(Boolean.FALSE, gson.fromJson("0", Boolean.class));
   }
 
-  public void testOverridePrimitiveBooleanAdapter() {
+  @Test
+  void testOverridePrimitiveBooleanAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(boolean.class, booleanAsIntAdapter)
         .create();
@@ -67,7 +71,8 @@ public void testOverridePrimitiveBooleanAdapter() {
     assertEquals("0", gson.toJson(false, boolean.class));
   }
 
-  public void testOverrideStringAdapter() {
+  @Test
+  void testOverrideStringAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(String.class, swapCaseStringAdapter)
         .create();
diff --git a/gson/src/test/java/com/google/gson/ParameterizedTypeFixtures.java b/gson/src/test/java/com/google/gson/ParameterizedTypeFixtures.java
index 0959ee4293..e370de2cb7 100644
--- a/gson/src/test/java/com/google/gson/ParameterizedTypeFixtures.java
+++ b/gson/src/test/java/com/google/gson/ParameterizedTypeFixtures.java
@@ -17,7 +17,6 @@
 package com.google.gson;
 
 import com.google.gson.internal.$Gson$Types;
-
 import com.google.gson.internal.Primitives;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
diff --git a/gson/src/test/java/com/google/gson/ParameterizedTypeTest.java b/gson/src/test/java/com/google/gson/ParameterizedTypeTest.java
index 24d78e89d8..c8e31212e7 100644
--- a/gson/src/test/java/com/google/gson/ParameterizedTypeTest.java
+++ b/gson/src/test/java/com/google/gson/ParameterizedTypeTest.java
@@ -16,14 +16,17 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
 import com.google.gson.internal.$Gson$Types;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for {@code ParameterizedType}s created by the {@link $Gson$Types} class.
@@ -31,16 +34,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ParameterizedTypeTest extends TestCase {
+class ParameterizedTypeTest {
   private ParameterizedType ourType;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     ourType = $Gson$Types.newParameterizedTypeWithOwner(null, List.class, String.class);
   }
 
-  public void testOurTypeFunctionality() throws Exception {
+  @Test
+  void testOurTypeFunctionality() throws Exception {
     Type parameterizedType = new TypeToken<List<String>>() {}.getType();
     assertNull(ourType.getOwnerType());
     assertEquals(String.class, ourType.getActualTypeArguments()[0]);
@@ -49,7 +52,8 @@ public void testOurTypeFunctionality() throws Exception {
     assertEquals(parameterizedType.hashCode(), ourType.hashCode());
   }
 
-  public void testNotEquals() throws Exception {
+  @Test
+  void testNotEquals() throws Exception {
     Type differentParameterizedType = new TypeToken<List<Integer>>() {}.getType();
     assertFalse(differentParameterizedType.equals(ourType));
     assertFalse(ourType.equals(differentParameterizedType));
diff --git a/gson/src/test/java/com/google/gson/ToNumberPolicyTest.java b/gson/src/test/java/com/google/gson/ToNumberPolicyTest.java
index db9898d47d..a85cc551f9 100644
--- a/gson/src/test/java/com/google/gson/ToNumberPolicyTest.java
+++ b/gson/src/test/java/com/google/gson/ToNumberPolicyTest.java
@@ -16,16 +16,20 @@
 
 package com.google.gson;
 
-import java.io.IOException;
-import java.io.StringReader;
-import java.math.BigDecimal;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.internal.LazilyParsedNumber;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.MalformedJsonException;
-import junit.framework.TestCase;
+import java.io.IOException;
+import java.io.StringReader;
+import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
 
-public class ToNumberPolicyTest extends TestCase {
-  public void testDouble() throws IOException {
+class ToNumberPolicyTest {
+  @Test
+  void testDouble() throws IOException {
     ToNumberStrategy strategy = ToNumberPolicy.DOUBLE;
     assertEquals(10.1, strategy.readNumber(fromString("10.1")));
     assertEquals(3.141592653589793D, strategy.readNumber(fromString("3.141592653589793238462643383279")));
@@ -42,14 +46,16 @@ public void testDouble() throws IOException {
     }
   }
 
-  public void testLazilyParsedNumber() throws IOException {
+  @Test
+  void testLazilyParsedNumber() throws IOException {
     ToNumberStrategy strategy = ToNumberPolicy.LAZILY_PARSED_NUMBER;
     assertEquals(new LazilyParsedNumber("10.1"), strategy.readNumber(fromString("10.1")));
     assertEquals(new LazilyParsedNumber("3.141592653589793238462643383279"), strategy.readNumber(fromString("3.141592653589793238462643383279")));
     assertEquals(new LazilyParsedNumber("1e400"), strategy.readNumber(fromString("1e400")));
   }
 
-  public void testLongOrDouble() throws IOException {
+  @Test
+  void testLongOrDouble() throws IOException {
     ToNumberStrategy strategy = ToNumberPolicy.LONG_OR_DOUBLE;
     assertEquals(10L, strategy.readNumber(fromString("10")));
     assertEquals(10.1, strategy.readNumber(fromString("10.1")));
@@ -90,7 +96,8 @@ public void testLongOrDouble() throws IOException {
     }
   }
 
-  public void testBigDecimal() throws IOException {
+  @Test
+  void testBigDecimal() throws IOException {
     ToNumberStrategy strategy = ToNumberPolicy.BIG_DECIMAL;
     assertEquals(new BigDecimal("10.1"), strategy.readNumber(fromString("10.1")));
     assertEquals(new BigDecimal("3.141592653589793238462643383279"), strategy.readNumber(fromString("3.141592653589793238462643383279")));
@@ -104,7 +111,8 @@ public void testBigDecimal() throws IOException {
     }
   }
 
-  public void testNullsAreNeverExpected() throws IOException {
+  @Test
+  void testNullsAreNeverExpected() throws IOException {
     try {
       ToNumberPolicy.DOUBLE.readNumber(fromString("null"));
       fail();
diff --git a/gson/src/test/java/com/google/gson/VersionExclusionStrategyTest.java b/gson/src/test/java/com/google/gson/VersionExclusionStrategyTest.java
index d878850ec9..29166a9f0b 100644
--- a/gson/src/test/java/com/google/gson/VersionExclusionStrategyTest.java
+++ b/gson/src/test/java/com/google/gson/VersionExclusionStrategyTest.java
@@ -16,31 +16,37 @@
 
 package com.google.gson;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.annotations.Since;
 import com.google.gson.internal.Excluder;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for the {@link Excluder} class.
  *
  * @author Joel Leitch
  */
-public class VersionExclusionStrategyTest extends TestCase {
+class VersionExclusionStrategyTest {
   private static final double VERSION = 5.0D;
 
-  public void testClassAndFieldAreAtSameVersion() throws Exception {
+  @Test
+  void testClassAndFieldAreAtSameVersion() throws Exception {
     Excluder excluder = Excluder.DEFAULT.withVersion(VERSION);
     assertFalse(excluder.excludeClass(MockObject.class, true));
     assertFalse(excluder.excludeField(MockObject.class.getField("someField"), true));
   }
 
-  public void testClassAndFieldAreBehindInVersion() throws Exception {
+  @Test
+  void testClassAndFieldAreBehindInVersion() throws Exception {
     Excluder excluder = Excluder.DEFAULT.withVersion(VERSION + 1);
     assertFalse(excluder.excludeClass(MockObject.class, true));
     assertFalse(excluder.excludeField(MockObject.class.getField("someField"), true));
   }
 
-  public void testClassAndFieldAreAheadInVersion() throws Exception {
+  @Test
+  void testClassAndFieldAreAheadInVersion() throws Exception {
     Excluder excluder = Excluder.DEFAULT.withVersion(VERSION - 1);
     assertTrue(excluder.excludeClass(MockObject.class, true));
     assertTrue(excluder.excludeField(MockObject.class.getField("someField"), true));
diff --git a/gson/src/test/java/com/google/gson/common/MoreAsserts.java b/gson/src/test/java/com/google/gson/common/MoreAsserts.java
index f409480d67..7eb5518f9a 100644
--- a/gson/src/test/java/com/google/gson/common/MoreAsserts.java
+++ b/gson/src/test/java/com/google/gson/common/MoreAsserts.java
@@ -16,7 +16,10 @@
 
 package com.google.gson.common;
 
-import org.junit.Assert;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import java.util.Collection;
 
@@ -39,14 +42,14 @@ public static <T> void assertContains(Collection<T> collection, T value) {
         return;
       }
     }
-    Assert.fail(value + " not present in " + collection);
+    fail(value + " not present in " + collection);
   }
 
   public static void assertEqualsAndHashCode(Object a, Object b) {
-    Assert.assertTrue(a.equals(b));
-    Assert.assertTrue(b.equals(a));
-    Assert.assertEquals(a.hashCode(), b.hashCode());
-    Assert.assertFalse(a.equals(null));
-    Assert.assertFalse(a.equals(new Object()));
+    assertTrue(a.equals(b));
+    assertTrue(b.equals(a));
+    assertEquals(a.hashCode(), b.hashCode());
+    assertFalse(a.equals(null));
+    assertFalse(a.equals(new Object()));
   }
 }
diff --git a/gson/src/test/java/com/google/gson/common/TestTypes.java b/gson/src/test/java/com/google/gson/common/TestTypes.java
index 11d3d0abe8..8327fa06af 100644
--- a/gson/src/test/java/com/google/gson/common/TestTypes.java
+++ b/gson/src/test/java/com/google/gson/common/TestTypes.java
@@ -16,9 +16,6 @@
 
 package com.google.gson.common;
 
-import java.lang.reflect.Type;
-import java.util.Collection;
-
 import com.google.gson.JsonDeserializationContext;
 import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonElement;
@@ -28,6 +25,8 @@
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import com.google.gson.annotations.SerializedName;
+import java.lang.reflect.Type;
+import java.util.Collection;
 
 /**
  * Types used for testing JSON serialization and deserialization
diff --git a/gson/src/test/java/com/google/gson/functional/ArrayTest.java b/gson/src/test/java/com/google/gson/functional/ArrayTest.java
index dd0b628676..cd97fc68c2 100644
--- a/gson/src/test/java/com/google/gson/functional/ArrayTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ArrayTest.java
@@ -16,47 +16,53 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonParseException;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.common.TestTypes.ClassWithObjects;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-import static org.junit.Assert.assertArrayEquals;
-
 import java.lang.reflect.Type;
 import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Collection;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 /**
  * Functional tests for Json serialization and deserialization of arrays.
  *
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ArrayTest extends TestCase {
+class ArrayTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testTopLevelArrayOfIntsSerialization() {
+  @Test
+  void testTopLevelArrayOfIntsSerialization() {
     int[] target = {1, 2, 3, 4, 5, 6, 7, 8, 9};
     assertEquals("[1,2,3,4,5,6,7,8,9]", gson.toJson(target));
   }
 
-  public void testTopLevelArrayOfIntsDeserialization() {
+  @Test
+  void testTopLevelArrayOfIntsDeserialization() {
     int[] expected = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
     int[] actual = gson.fromJson("[1,2,3,4,5,6,7,8,9]", int[].class);
     assertArrayEquals(expected, actual);
   }
 
-  public void testInvalidArrayDeserialization() {
+  @Test
+  void testInvalidArrayDeserialization() {
     String json = "[1, 2 3, 4, 5]";
     try {
       gson.fromJson(json, int[].class);
@@ -65,12 +71,14 @@ public void testInvalidArrayDeserialization() {
     }
   }
 
-  public void testEmptyArraySerialization() {
+  @Test
+  void testEmptyArraySerialization() {
     int[] target = {};
     assertEquals("[]", gson.toJson(target));
   }
 
-  public void testEmptyArrayDeserialization() {
+  @Test
+  void testEmptyArrayDeserialization() {
     int[] actualObject = gson.fromJson("[]", int[].class);
     assertTrue(actualObject.length == 0);
 
@@ -81,14 +89,16 @@ public void testEmptyArrayDeserialization() {
     assertTrue(actualObject.length == 0);
   }
 
-  public void testNullsInArraySerialization() {
+  @Test
+  void testNullsInArraySerialization() {
     String[] array = {"foo", null, "bar"};
     String expected = "[\"foo\",null,\"bar\"]";
     String json = gson.toJson(array);
     assertEquals(expected, json);
   }
 
-  public void testNullsInArrayDeserialization() {
+  @Test
+  void testNullsInArrayDeserialization() {
     String json = "[\"foo\",null,\"bar\"]";
     String[] expected = {"foo", null, "bar"};
     String[] target = gson.fromJson(json, expected.getClass());
@@ -97,19 +107,22 @@ public void testNullsInArrayDeserialization() {
     }
   }
 
-  public void testSingleNullInArraySerialization() {
+  @Test
+  void testSingleNullInArraySerialization() {
     BagOfPrimitives[] array = new BagOfPrimitives[1];
     array[0] = null;
     String json = gson.toJson(array);
     assertEquals("[null]", json);
   }
 
-  public void testSingleNullInArrayDeserialization() {
+  @Test
+  void testSingleNullInArrayDeserialization() {
     BagOfPrimitives[] array = gson.fromJson("[null]", BagOfPrimitives[].class);
     assertNull(array[0]);
   }
 
-  public void testNullsInArrayWithSerializeNullPropertySetSerialization() {
+  @Test
+  void testNullsInArrayWithSerializeNullPropertySetSerialization() {
     gson = new GsonBuilder().serializeNulls().create();
     String[] array = {"foo", null, "bar"};
     String expected = "[\"foo\",null,\"bar\"]";
@@ -117,37 +130,42 @@ public void testNullsInArrayWithSerializeNullPropertySetSerialization() {
     assertEquals(expected, json);
   }
 
-  public void testArrayOfStringsSerialization() {
+  @Test
+  void testArrayOfStringsSerialization() {
     String[] target = {"Hello", "World"};
     assertEquals("[\"Hello\",\"World\"]", gson.toJson(target));
   }
 
-  public void testArrayOfStringsDeserialization() {
+  @Test
+  void testArrayOfStringsDeserialization() {
     String json = "[\"Hello\",\"World\"]";
     String[] target = gson.fromJson(json, String[].class);
     assertEquals("Hello", target[0]);
     assertEquals("World", target[1]);
   }
 
-  public void testSingleStringArraySerialization() throws Exception {
+  @Test
+  void testSingleStringArraySerialization() throws Exception {
     String[] s = { "hello" };
     String output = gson.toJson(s);
     assertEquals("[\"hello\"]", output);
   }
 
-  public void testSingleStringArrayDeserialization() throws Exception {
+  @Test
+  void testSingleStringArrayDeserialization() throws Exception {
     String json = "[\"hello\"]";
     String[] arrayType = gson.fromJson(json, String[].class);
     assertEquals(1, arrayType.length);
     assertEquals("hello", arrayType[0]);
   }
 
-  @SuppressWarnings("unchecked")
-  public void testArrayOfCollectionSerialization() throws Exception {
+  @Test
+  void testArrayOfCollectionSerialization() throws Exception {
     StringBuilder sb = new StringBuilder("[");
     int arraySize = 3;
 
     Type typeToSerialize = new TypeToken<Collection<Integer>[]>() {}.getType();
+    @SuppressWarnings("unchecked")
     Collection<Integer>[] arrayOfCollection = new ArrayList[arraySize];
     for (int i = 0; i < arraySize; ++i) {
       int startValue = (3 * i) + 1;
@@ -167,7 +185,8 @@ public void testArrayOfCollectionSerialization() throws Exception {
     assertEquals(sb.toString(), json);
   }
 
-  public void testArrayOfCollectionDeserialization() throws Exception {
+  @Test
+  void testArrayOfCollectionDeserialization() throws Exception {
     String json = "[[1,2],[3,4]]";
     Type type = new TypeToken<Collection<Integer>[]>() {}.getType();
     Collection<Integer>[] target = gson.fromJson(json, type);
@@ -177,7 +196,8 @@ public void testArrayOfCollectionDeserialization() throws Exception {
     assertArrayEquals(new Integer[] { 3, 4 }, target[1].toArray(new Integer[0]));
   }
 
-  public void testArrayOfPrimitivesAsObjectsSerialization() throws Exception {
+  @Test
+  void testArrayOfPrimitivesAsObjectsSerialization() throws Exception {
     Object[] objs = new Object[] {1, "abc", 0.3f, 5L};
     String json = gson.toJson(objs);
     assertTrue(json.contains("abc"));
@@ -185,7 +205,8 @@ public void testArrayOfPrimitivesAsObjectsSerialization() throws Exception {
     assertTrue(json.contains("5"));
   }
 
-  public void testArrayOfPrimitivesAsObjectsDeserialization() throws Exception {
+  @Test
+  void testArrayOfPrimitivesAsObjectsDeserialization() throws Exception {
     String json = "[1,'abc',0.3,1.1,5]";
     Object[] objs = gson.fromJson(json, Object[].class);
     assertEquals(1, ((Number)objs[0]).intValue());
@@ -195,7 +216,8 @@ public void testArrayOfPrimitivesAsObjectsDeserialization() throws Exception {
     assertEquals(5, ((Number)objs[4]).shortValue());
   }
 
-  public void testObjectArrayWithNonPrimitivesSerialization() throws Exception {
+  @Test
+  void testObjectArrayWithNonPrimitivesSerialization() throws Exception {
     ClassWithObjects classWithObjects = new ClassWithObjects();
     BagOfPrimitives bagOfPrimitives = new BagOfPrimitives();
     String classWithObjectsJson = gson.toJson(classWithObjects);
@@ -208,13 +230,15 @@ public void testObjectArrayWithNonPrimitivesSerialization() throws Exception {
     assertTrue(json.contains(bagOfPrimitivesJson));
   }
 
-  public void testArrayOfNullSerialization() {
+  @Test
+  void testArrayOfNullSerialization() {
     Object[] array = new Object[] {null};
     String json = gson.toJson(array);
     assertEquals("[null]", json);
   }
 
-  public void testArrayOfNullDeserialization() {
+  @Test
+  void testArrayOfNullDeserialization() {
     String[] values = gson.fromJson("[null]", String[].class);
     assertNull(values[0]);
   }
@@ -222,7 +246,8 @@ public void testArrayOfNullDeserialization() {
   /**
    * Regression tests for Issue 272
    */
-  public void testMultidimenstionalArraysSerialization() {
+  @Test
+  void testMultidimenstionalArraysSerialization() {
     String[][] items = new String[][]{
         {"3m Co", "71.72", "0.02", "0.03", "4/2 12:00am", "Manufacturing"},
         {"Alcoa Inc", "29.01", "0.42", "1.47", "4/1 12:00am", "Manufacturing"}
@@ -232,7 +257,8 @@ public void testMultidimenstionalArraysSerialization() {
     assertTrue(json.contains("Manufacturing\"]]"));
   }
 
-  public void testMultiDimenstionalObjectArraysSerialization() {
+  @Test
+  void testMultiDimenstionalObjectArraysSerialization() {
     Object[][] array = new Object[][] { new Object[] { 1, 2 } };
     assertEquals("[[1,2]]", gson.toJson(array));
   }
@@ -240,7 +266,8 @@ public void testMultiDimenstionalObjectArraysSerialization() {
   /**
    * Regression test for Issue 205
    */
-  public void testMixingTypesInObjectArraySerialization() {
+  @Test
+  void testMixingTypesInObjectArraySerialization() {
     Object[] array = new Object[] { 1, 2, new Object[] { "one", "two", 3 } };
     assertEquals("[1,2,[\"one\",\"two\",3]]", gson.toJson(array));
   }
@@ -248,7 +275,8 @@ public void testMixingTypesInObjectArraySerialization() {
   /**
    * Regression tests for Issue 272
    */
-  public void testMultidimenstionalArraysDeserialization() {
+  @Test
+  void testMultidimenstionalArraysDeserialization() {
     String json = "[['3m Co','71.72','0.02','0.03','4/2 12:00am','Manufacturing'],"
       + "['Alcoa Inc','29.01','0.42','1.47','4/1 12:00am','Manufacturing']]";
     String[][] items = gson.fromJson(json, String[][].class);
@@ -257,7 +285,8 @@ public void testMultidimenstionalArraysDeserialization() {
   }
 
   /** http://code.google.com/p/google-gson/issues/detail?id=342 */
-  public void testArrayElementsAreArrays() {
+  @Test
+  void testArrayElementsAreArrays() {
     Object[] stringArrays = {
         new String[] {"test1", "test2"},
         new String[] {"test3", "test4"}
diff --git a/gson/src/test/java/com/google/gson/functional/CircularReferenceTest.java b/gson/src/test/java/com/google/gson/functional/CircularReferenceTest.java
index d352e2418c..ad5678cff9 100644
--- a/gson/src/test/java/com/google/gson/functional/CircularReferenceTest.java
+++ b/gson/src/test/java/com/google/gson/functional/CircularReferenceTest.java
@@ -15,11 +15,10 @@
  */
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
-import java.util.ArrayList;
-import java.util.Collection;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -28,6 +27,11 @@
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import com.google.gson.common.TestTypes.ClassOverridingEquals;
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Collection;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests related to circular reference detection and error reporting.
@@ -35,16 +39,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class CircularReferenceTest extends TestCase {
+class CircularReferenceTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testCircularSerialization() throws Exception {
+  @Test
+  void testCircularSerialization() throws Exception {
     ContainsReferenceToSelfType a = new ContainsReferenceToSelfType();
     ContainsReferenceToSelfType b = new ContainsReferenceToSelfType();
     a.children.add(b);
@@ -56,7 +60,8 @@ public void testCircularSerialization() throws Exception {
     }
   }
 
-  public void testSelfReferenceIgnoredInSerialization() throws Exception {
+  @Test
+  void testSelfReferenceIgnoredInSerialization() throws Exception {
     ClassOverridingEquals objA = new ClassOverridingEquals();
     objA.ref = objA;
 
@@ -64,7 +69,8 @@ public void testSelfReferenceIgnoredInSerialization() throws Exception {
     assertFalse(json.contains("ref")); // self-reference is ignored
   }
 
-  public void testSelfReferenceArrayFieldSerialization() throws Exception {
+  @Test
+  void testSelfReferenceArrayFieldSerialization() throws Exception {
     ClassWithSelfReferenceArray objA = new ClassWithSelfReferenceArray();
     objA.children = new ClassWithSelfReferenceArray[]{objA};
 
@@ -75,10 +81,12 @@ public void testSelfReferenceArrayFieldSerialization() throws Exception {
     }
   }
 
-  public void testSelfReferenceCustomHandlerSerialization() throws Exception {
+  @Test
+  void testSelfReferenceCustomHandlerSerialization() throws Exception {
     ClassWithSelfReference obj = new ClassWithSelfReference();
     obj.child = obj;
     Gson gson = new GsonBuilder().registerTypeAdapter(ClassWithSelfReference.class, new JsonSerializer<ClassWithSelfReference>() {
+      @Override
       public JsonElement serialize(ClassWithSelfReference src, Type typeOfSrc,
           JsonSerializationContext context) {
         JsonObject obj = new JsonObject();
@@ -94,7 +102,8 @@ public JsonElement serialize(ClassWithSelfReference src, Type typeOfSrc,
     }
   }
 
-  public void testDirectedAcyclicGraphSerialization() throws Exception {
+  @Test
+  void testDirectedAcyclicGraphSerialization() throws Exception {
     ContainsReferenceToSelfType a = new ContainsReferenceToSelfType();
     ContainsReferenceToSelfType b = new ContainsReferenceToSelfType();
     ContainsReferenceToSelfType c = new ContainsReferenceToSelfType();
@@ -104,7 +113,8 @@ public void testDirectedAcyclicGraphSerialization() throws Exception {
     assertNotNull(gson.toJson(a));
   }
 
-  public void testDirectedAcyclicGraphDeserialization() throws Exception {
+  @Test
+  void testDirectedAcyclicGraphDeserialization() throws Exception {
     String json = "{\"children\":[{\"children\":[{\"children\":[]}]},{\"children\":[]}]}";
     ContainsReferenceToSelfType target = gson.fromJson(json, ContainsReferenceToSelfType.class);
     assertNotNull(target);
diff --git a/gson/src/test/java/com/google/gson/functional/CollectionTest.java b/gson/src/test/java/com/google/gson/functional/CollectionTest.java
index 261c5d02d3..19d97a48eb 100644
--- a/gson/src/test/java/com/google/gson/functional/CollectionTest.java
+++ b/gson/src/test/java/com/google/gson/functional/CollectionTest.java
@@ -16,6 +16,19 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
+import com.google.gson.common.TestTypes.BagOfPrimitives;
+import com.google.gson.reflect.TypeToken;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -30,18 +43,8 @@
 import java.util.Set;
 import java.util.Stack;
 import java.util.Vector;
-
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonPrimitive;
-import com.google.gson.JsonSerializationContext;
-import com.google.gson.JsonSerializer;
-import com.google.gson.common.TestTypes.BagOfPrimitives;
-import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-import static org.junit.Assert.assertArrayEquals;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for Json serialization and deserialization of collections.
@@ -49,23 +52,24 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class CollectionTest extends TestCase {
+class CollectionTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testTopLevelCollectionOfIntegersSerialization() {
+  @Test
+  void testTopLevelCollectionOfIntegersSerialization() {
     Collection<Integer> target = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);
     Type targetType = new TypeToken<Collection<Integer>>() {}.getType();
     String json = gson.toJson(target, targetType);
     assertEquals("[1,2,3,4,5,6,7,8,9]", json);
   }
 
-  public void testTopLevelCollectionOfIntegersDeserialization() {
+  @Test
+  void testTopLevelCollectionOfIntegersDeserialization() {
     String json = "[0,1,2,3,4,5,6,7,8,9]";
     Type collectionType = new TypeToken<Collection<Integer>>() { }.getType();
     Collection<Integer> target = gson.fromJson(json, collectionType);
@@ -73,7 +77,8 @@ public void testTopLevelCollectionOfIntegersDeserialization() {
     assertArrayEquals(expected, toIntArray(target));
   }
 
-  public void testTopLevelListOfIntegerCollectionsDeserialization() throws Exception {
+  @Test
+  void testTopLevelListOfIntegerCollectionsDeserialization() throws Exception {
     String json = "[[1,2,3],[4,5,6],[7,8,9]]";
     Type collectionType = new TypeToken<Collection<Collection<Integer>>>() {}.getType();
     List<Collection<Integer>> target = gson.fromJson(json, collectionType);
@@ -90,7 +95,8 @@ public void testTopLevelListOfIntegerCollectionsDeserialization() throws Excepti
     }
   }
 
-  public void testLinkedListSerialization() {
+  @Test
+  void testLinkedListSerialization() {
     List<String> list = new LinkedList<String>();
     list.add("a1");
     list.add("a2");
@@ -100,7 +106,8 @@ public void testLinkedListSerialization() {
     assertTrue(json.contains("a2"));
   }
 
-  public void testLinkedListDeserialization() {
+  @Test
+  void testLinkedListDeserialization() {
     String json = "['a1','a2']";
     Type linkedListType = new TypeToken<LinkedList<String>>() {}.getType();
     List<String> list = gson.fromJson(json, linkedListType);
@@ -108,7 +115,8 @@ public void testLinkedListDeserialization() {
     assertEquals("a2", list.get(1));
   }
 
-  public void testQueueSerialization() {
+  @Test
+  void testQueueSerialization() {
     Queue<String> queue = new LinkedList<String>();
     queue.add("a1");
     queue.add("a2");
@@ -118,7 +126,8 @@ public void testQueueSerialization() {
     assertTrue(json.contains("a2"));
   }
 
-  public void testQueueDeserialization() {
+  @Test
+  void testQueueDeserialization() {
     String json = "['a1','a2']";
     Type queueType = new TypeToken<Queue<String>>() {}.getType();
     Queue<String> queue = gson.fromJson(json, queueType);
@@ -127,7 +136,8 @@ public void testQueueDeserialization() {
     assertEquals("a2", queue.element());
   }
 
-  public void testPriorityQueue() throws Exception {
+  @Test
+  void testPriorityQueue() throws Exception {
     Type type = new TypeToken<PriorityQueue<Integer>>(){}.getType();
     PriorityQueue<Integer> queue = gson.fromJson("[10, 20, 22]", type);
     assertEquals(3, queue.size());
@@ -138,7 +148,8 @@ public void testPriorityQueue() throws Exception {
     assertEquals("[10,20,22]", json);
   }
 
-  public void testVector() {
+  @Test
+  void testVector() {
     Type type = new TypeToken<Vector<Integer>>(){}.getType();
     Vector<Integer> target = gson.fromJson("[10, 20, 31]", type);
     assertEquals(3, target.size());
@@ -149,7 +160,8 @@ public void testVector() {
     assertEquals("[10,20,31]", json);
   }
 
-  public void testStack() {
+  @Test
+  void testStack() {
     Type type = new TypeToken<Stack<Integer>>(){}.getType();
     Stack<Integer> target = gson.fromJson("[11, 13, 17]", type);
     assertEquals(3, target.size());
@@ -160,7 +172,8 @@ public void testStack() {
     assertEquals("[11,13,17]", json);
   }
 
-  public void testNullsInListSerialization() {
+  @Test
+  void testNullsInListSerialization() {
     List<String> list = new ArrayList<String>();
     list.add("foo");
     list.add(null);
@@ -171,7 +184,8 @@ public void testNullsInListSerialization() {
     assertEquals(expected, json);
   }
 
-  public void testNullsInListDeserialization() {
+  @Test
+  void testNullsInListDeserialization() {
     List<String> expected = new ArrayList<String>();
     expected.add("foo");
     expected.add(null);
@@ -184,7 +198,8 @@ public void testNullsInListDeserialization() {
     }
   }
 
-  public void testCollectionOfObjectSerialization() {
+  @Test
+  void testCollectionOfObjectSerialization() {
     List<Object> target = new ArrayList<Object>();
     target.add("Hello");
     target.add("World");
@@ -194,7 +209,8 @@ public void testCollectionOfObjectSerialization() {
     assertEquals("[\"Hello\",\"World\"]", gson.toJson(target, type));
   }
 
-  public void testCollectionOfObjectWithNullSerialization() {
+  @Test
+  void testCollectionOfObjectWithNullSerialization() {
     List<Object> target = new ArrayList<Object>();
     target.add("Hello");
     target.add(null);
@@ -205,14 +221,16 @@ public void testCollectionOfObjectWithNullSerialization() {
     assertEquals("[\"Hello\",null,\"World\"]", gson.toJson(target, type));
   }
 
-  public void testCollectionOfStringsSerialization() {
+  @Test
+  void testCollectionOfStringsSerialization() {
     List<String> target = new ArrayList<String>();
     target.add("Hello");
     target.add("World");
     assertEquals("[\"Hello\",\"World\"]", gson.toJson(target));
   }
 
-  public void testCollectionOfBagOfPrimitivesSerialization() {
+  @Test
+  void testCollectionOfBagOfPrimitivesSerialization() {
     List<BagOfPrimitives> target = new ArrayList<BagOfPrimitives>();
     BagOfPrimitives objA = new BagOfPrimitives(3L, 1, true, "blah");
     BagOfPrimitives objB = new BagOfPrimitives(2L, 6, false, "blahB");
@@ -227,7 +245,8 @@ public void testCollectionOfBagOfPrimitivesSerialization() {
     }
   }
 
-  public void testCollectionOfStringsDeserialization() {
+  @Test
+  void testCollectionOfStringsDeserialization() {
     String json = "[\"Hello\",\"World\"]";
     Type collectionType = new TypeToken<Collection<String>>() { }.getType();
     Collection<String> target = gson.fromJson(json, collectionType);
@@ -236,40 +255,42 @@ public void testCollectionOfStringsDeserialization() {
     assertTrue(target.contains("World"));
   }
 
-  public void testRawCollectionOfIntegersSerialization() {
+  @Test
+  void testRawCollectionOfIntegersSerialization() {
     Collection<Integer> target = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);
     assertEquals("[1,2,3,4,5,6,7,8,9]", gson.toJson(target));
   }
 
-  @SuppressWarnings("rawtypes")
-  public void testRawCollectionSerialization() {
+  @Test
+  void testRawCollectionSerialization() {
     BagOfPrimitives bag1 = new BagOfPrimitives();
-    Collection target = Arrays.asList(bag1, bag1);
+    Collection<?> target = Arrays.asList(bag1, bag1);
     String json = gson.toJson(target);
     assertTrue(json.contains(bag1.getExpectedJson()));
   }
 
-  @SuppressWarnings("rawtypes")
-  public void testRawCollectionDeserializationNotAlllowed() {
+  @Test
+  void testRawCollectionDeserializationNotAlllowed() {
     String json = "[0,1,2,3,4,5,6,7,8,9]";
-    Collection integers = gson.fromJson(json, Collection.class);
+    Collection<?> integers = gson.fromJson(json, Collection.class);
     // JsonReader converts numbers to double by default so we need a floating point comparison
     assertEquals(Arrays.asList(0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0), integers);
 
     json = "[\"Hello\", \"World\"]";
-    Collection strings = gson.fromJson(json, Collection.class);
+    Collection<?> strings = gson.fromJson(json, Collection.class);
     assertTrue(strings.contains("Hello"));
     assertTrue(strings.contains("World"));
   }
 
-  @SuppressWarnings({"rawtypes", "unchecked"})
-  public void testRawCollectionOfBagOfPrimitivesNotAllowed() {
+  @Test
+  void testRawCollectionOfBagOfPrimitivesNotAllowed() {
     BagOfPrimitives bag = new BagOfPrimitives(10, 20, false, "stringValue");
     String json = '[' + bag.getExpectedJson() + ',' + bag.getExpectedJson() + ']';
-    Collection target = gson.fromJson(json, Collection.class);
+    Collection<?> target = gson.fromJson(json, Collection.class);
     assertEquals(2, target.size());
     for (Object bag1 : target) {
       // Gson 2.0 converts raw objects into maps
+      @SuppressWarnings("unchecked")
       Map<String, Object> values = (Map<String, Object>) bag1;
       assertTrue(values.containsValue(10.0));
       assertTrue(values.containsValue(20.0));
@@ -277,7 +298,8 @@ public void testRawCollectionOfBagOfPrimitivesNotAllowed() {
     }
   }
 
-  public void testWildcardPrimitiveCollectionSerilaization() throws Exception {
+  @Test
+  void testWildcardPrimitiveCollectionSerilaization() throws Exception {
     Collection<? extends Integer> target = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);
     Type collectionType = new TypeToken<Collection<? extends Integer>>() { }.getType();
     String json = gson.toJson(target, collectionType);
@@ -287,7 +309,8 @@ public void testWildcardPrimitiveCollectionSerilaization() throws Exception {
     assertEquals("[1,2,3,4,5,6,7,8,9]", json);
   }
 
-  public void testWildcardPrimitiveCollectionDeserilaization() throws Exception {
+  @Test
+  void testWildcardPrimitiveCollectionDeserilaization() throws Exception {
     String json = "[1,2,3,4,5,6,7,8,9]";
     Type collectionType = new TypeToken<Collection<? extends Integer>>() { }.getType();
     Collection<? extends Integer> target = gson.fromJson(json, collectionType);
@@ -296,7 +319,8 @@ public void testWildcardPrimitiveCollectionDeserilaization() throws Exception {
     assertTrue(target.contains(9));
   }
 
-  public void testWildcardCollectionField() throws Exception {
+  @Test
+  void testWildcardCollectionField() throws Exception {
     Collection<BagOfPrimitives> collection = new ArrayList<BagOfPrimitives>();
     BagOfPrimitives objA = new BagOfPrimitives(3L, 1, true, "blah");
     BagOfPrimitives objB = new BagOfPrimitives(2L, 6, false, "blahB");
@@ -315,7 +339,8 @@ public void testWildcardCollectionField() throws Exception {
     assertTrue(deserializedCollection.contains(objB));
   }
 
-  public void testFieldIsArrayList() {
+  @Test
+  void testFieldIsArrayList() {
     HasArrayListField object = new HasArrayListField();
     object.longs.add(1L);
     object.longs.add(3L);
@@ -324,10 +349,12 @@ public void testFieldIsArrayList() {
     HasArrayListField copy = gson.fromJson("{\"longs\":[1,3]}", HasArrayListField.class);
     assertEquals(Arrays.asList(1L, 3L), copy.longs);
   }
-  
-  public void testUserCollectionTypeAdapter() {
+
+  @Test
+  void testUserCollectionTypeAdapter() {
     Type listOfString = new TypeToken<List<String>>() {}.getType();
     Object stringListSerializer = new JsonSerializer<List<String>>() {
+      @Override
       public JsonElement serialize(List<String> src, Type typeOfSrc,
           JsonSerializationContext context) {
         return new JsonPrimitive(src.get(0) + ";" + src.get(1));
@@ -376,7 +403,9 @@ private static class Entry {
       this.value = value;
     }
   }
-  public void testSetSerialization() {
+
+  @Test
+  void testSetSerialization() {
     Set<Entry> set = new HashSet<Entry>();
     set.add(new Entry(1));
     set.add(new Entry(2));
@@ -384,7 +413,9 @@ public void testSetSerialization() {
     assertTrue(json.contains("1"));
     assertTrue(json.contains("2"));
   }
-  public void testSetDeserialization() {
+
+  @Test
+  void testSetDeserialization() {
     String json = "[{value:1},{value:2}]";
     Type type = new TypeToken<Set<Entry>>() {}.getType();
     Set<Entry> set = gson.fromJson(json, type);
@@ -398,7 +429,8 @@ private class BigClass { private Map<String, ? extends List<SmallClass>> inBig;
 
   private class SmallClass { private String inSmall; }
 
-  public void testIssue1107() {
+  @Test
+  void testIssue1107() {
     String json = "{\n" +
             "  \"inBig\": {\n" +
             "    \"key\": [\n" +
diff --git a/gson/src/test/java/com/google/gson/functional/ConcurrencyTest.java b/gson/src/test/java/com/google/gson/functional/ConcurrencyTest.java
index 2dccf4b61a..5d6e6c7f10 100644
--- a/gson/src/test/java/com/google/gson/functional/ConcurrencyTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ConcurrencyTest.java
@@ -15,14 +15,15 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import com.google.gson.Gson;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.atomic.AtomicBoolean;
-
-import junit.framework.TestCase;
-
-import com.google.gson.Gson;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Tests for ensuring Gson thread-safety.
@@ -30,12 +31,11 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ConcurrencyTest extends TestCase {
+class ConcurrencyTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
@@ -43,34 +43,15 @@ protected void setUp() throws Exception {
    * Source-code based on
    * http://groups.google.com/group/google-gson/browse_thread/thread/563bb51ee2495081
    */
-  public void testSingleThreadSerialization() { 
-    MyObject myObj = new MyObject(); 
-    for (int i = 0; i < 10; i++) { 
-      gson.toJson(myObj); 
-    } 
-  } 
-
-  /**
-   * Source-code based on
-   * http://groups.google.com/group/google-gson/browse_thread/thread/563bb51ee2495081
-   */
-  public void testSingleThreadDeserialization() { 
-    for (int i = 0; i < 10; i++) { 
-      gson.fromJson("{'a':'hello','b':'world','i':1}", MyObject.class); 
-    } 
-  } 
-
-  /**
-   * Source-code based on
-   * http://groups.google.com/group/google-gson/browse_thread/thread/563bb51ee2495081
-   */
-  public void testMultiThreadSerialization() throws InterruptedException {
+  @Test
+  void testMultiThreadSerialization() throws InterruptedException {
     final CountDownLatch startLatch = new CountDownLatch(1);
     final CountDownLatch finishedLatch = new CountDownLatch(10);
     final AtomicBoolean failed = new AtomicBoolean(false);
     ExecutorService executor = Executors.newFixedThreadPool(10);
     for (int taskCount = 0; taskCount < 10; taskCount++) {
       executor.execute(new Runnable() {
+        @Override
         public void run() {
           MyObject myObj = new MyObject();
           try {
@@ -95,13 +76,15 @@ public void run() {
    * Source-code based on
    * http://groups.google.com/group/google-gson/browse_thread/thread/563bb51ee2495081
    */
-  public void testMultiThreadDeserialization() throws InterruptedException {
+  @Test
+  void testMultiThreadDeserialization() throws InterruptedException {
     final CountDownLatch startLatch = new CountDownLatch(1);
     final CountDownLatch finishedLatch = new CountDownLatch(10);
     final AtomicBoolean failed = new AtomicBoolean(false);
     ExecutorService executor = Executors.newFixedThreadPool(10);
     for (int taskCount = 0; taskCount < 10; taskCount++) {
       executor.execute(new Runnable() {
+        @Override
         public void run() {
           try {
             startLatch.await();
diff --git a/gson/src/test/java/com/google/gson/functional/CustomDeserializerTest.java b/gson/src/test/java/com/google/gson/functional/CustomDeserializerTest.java
index 8134ae2d19..3ce5d67068 100644
--- a/gson/src/test/java/com/google/gson/functional/CustomDeserializerTest.java
+++ b/gson/src/test/java/com/google/gson/functional/CustomDeserializerTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -25,10 +28,9 @@
 import com.google.gson.JsonParseException;
 import com.google.gson.common.TestTypes.Base;
 import com.google.gson.common.TestTypes.ClassWithBaseField;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.Type;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional Test exercising custom deserialization only. When test applies to both
@@ -36,19 +38,19 @@
  *
  * @author Joel Leitch
  */
-public class CustomDeserializerTest extends TestCase {
+class CustomDeserializerTest {
   private static final String DEFAULT_VALUE = "test123";
   private static final String SUFFIX = "blah";
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder().registerTypeAdapter(DataHolder.class, new DataHolderDeserializer()).create();
   }
 
-  public void testDefaultConstructorNotCalledOnObject() throws Exception {
+  @Test
+  void testDefaultConstructorNotCalledOnObject() throws Exception {
     DataHolder data = new DataHolder(DEFAULT_VALUE);
     String json = gson.toJson(data);
 
@@ -56,7 +58,8 @@ public void testDefaultConstructorNotCalledOnObject() throws Exception {
     assertEquals(DEFAULT_VALUE + SUFFIX, actual.getData());
   }
 
-  public void testDefaultConstructorNotCalledOnField() throws Exception {
+  @Test
+  void testDefaultConstructorNotCalledOnField() throws Exception {
     DataHolderWrapper dataWrapper = new DataHolderWrapper(new DataHolder(DEFAULT_VALUE));
     String json = gson.toJson(dataWrapper);
 
@@ -110,7 +113,8 @@ public DataHolder deserialize(JsonElement json, Type typeOfT, JsonDeserializatio
     }
   }
 
-  public void testJsonTypeFieldBasedDeserialization() {
+  @Test
+  void testJsonTypeFieldBasedDeserialization() {
     String json = "{field1:'abc',field2:'def',__type__:'SUB_TYPE1'}";
     Gson gson = new GsonBuilder().registerTypeAdapter(MyBase.class, new JsonDeserializer<MyBase>() {
       @Override public MyBase deserialize(JsonElement json, Type pojoType,
@@ -134,7 +138,7 @@ private enum SubTypes {
     private SubTypes(Type subClass) {
       this.subClass = subClass;
     }
-    public Type getSubclass() {
+    Type getSubclass() {
       return subClass;
     }
   }
@@ -148,7 +152,8 @@ private static class SubType2 extends MyBase {
     String field2;
   }
 
-  public void testCustomDeserializerReturnsNullForTopLevelObject() {
+  @Test
+  void testCustomDeserializerReturnsNullForTopLevelObject() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Base.class, new JsonDeserializer<Base>() {
         @Override
@@ -162,7 +167,8 @@ public Base deserialize(JsonElement json, Type typeOfT, JsonDeserializationConte
     assertNull(target);
   }
 
-  public void testCustomDeserializerReturnsNull() {
+  @Test
+  void testCustomDeserializerReturnsNull() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Base.class, new JsonDeserializer<Base>() {
         @Override
@@ -176,7 +182,8 @@ public Base deserialize(JsonElement json, Type typeOfT, JsonDeserializationConte
     assertNull(target.base);
   }
 
-  public void testCustomDeserializerReturnsNullForArrayElements() {
+  @Test
+  void testCustomDeserializerReturnsNullForArrayElements() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Base.class, new JsonDeserializer<Base>() {
         @Override
@@ -191,7 +198,8 @@ public Base deserialize(JsonElement json, Type typeOfT, JsonDeserializationConte
     assertNull(target[1]);
   }
 
-  public void testCustomDeserializerReturnsNullForArrayElementsForArrayField() {
+  @Test
+  void testCustomDeserializerReturnsNullForArrayElementsForArrayField() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Base.class, new JsonDeserializer<Base>() {
         @Override
diff --git a/gson/src/test/java/com/google/gson/functional/CustomSerializerTest.java b/gson/src/test/java/com/google/gson/functional/CustomSerializerTest.java
index c8095463a3..405a4338a9 100644
--- a/gson/src/test/java/com/google/gson/functional/CustomSerializerTest.java
+++ b/gson/src/test/java/com/google/gson/functional/CustomSerializerTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonArray;
@@ -29,10 +32,8 @@
 import com.google.gson.common.TestTypes.ClassWithBaseField;
 import com.google.gson.common.TestTypes.Sub;
 import com.google.gson.common.TestTypes.SubSerializer;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.Type;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional Test exercising custom serialization only.  When test applies to both
@@ -40,9 +41,10 @@
  *
  * @author Inderjeet Singh
  */
-public class CustomSerializerTest extends TestCase {
+class CustomSerializerTest {
 
-   public void testBaseClassSerializerInvokedForBaseClassFields() {
+  @Test
+   void testBaseClassSerializerInvokedForBaseClassFields() {
      Gson gson = new GsonBuilder()
          .registerTypeAdapter(Base.class, new BaseSerializer())
          .registerTypeAdapter(Sub.class, new SubSerializer())
@@ -53,7 +55,8 @@ public void testBaseClassSerializerInvokedForBaseClassFields() {
      assertEquals(BaseSerializer.NAME, base.get(Base.SERIALIZER_KEY).getAsString());
    }
 
-   public void testSubClassSerializerInvokedForBaseClassFieldsHoldingSubClassInstances() {
+   @Test
+   void testSubClassSerializerInvokedForBaseClassFieldsHoldingSubClassInstances() {
      Gson gson = new GsonBuilder()
          .registerTypeAdapter(Base.class, new BaseSerializer())
          .registerTypeAdapter(Sub.class, new SubSerializer())
@@ -64,7 +67,8 @@ public void testSubClassSerializerInvokedForBaseClassFieldsHoldingSubClassInstan
      assertEquals(SubSerializer.NAME, base.get(Base.SERIALIZER_KEY).getAsString());
    }
 
-   public void testSubClassSerializerInvokedForBaseClassFieldsHoldingArrayOfSubClassInstances() {
+   @Test
+   void testSubClassSerializerInvokedForBaseClassFieldsHoldingArrayOfSubClassInstances() {
      Gson gson = new GsonBuilder()
          .registerTypeAdapter(Base.class, new BaseSerializer())
          .registerTypeAdapter(Sub.class, new SubSerializer())
@@ -78,7 +82,8 @@ public void testSubClassSerializerInvokedForBaseClassFieldsHoldingArrayOfSubClas
      }
    }
 
-   public void testBaseClassSerializerInvokedForBaseClassFieldsHoldingSubClassInstances() {
+   @Test
+   void testBaseClassSerializerInvokedForBaseClassFieldsHoldingSubClassInstances() {
      Gson gson = new GsonBuilder()
          .registerTypeAdapter(Base.class, new BaseSerializer())
          .create();
@@ -88,9 +93,11 @@ public void testBaseClassSerializerInvokedForBaseClassFieldsHoldingSubClassInsta
      assertEquals(BaseSerializer.NAME, base.get(Base.SERIALIZER_KEY).getAsString());
    }
 
-   public void testSerializerReturnsNull() {
+   @Test
+   void testSerializerReturnsNull() {
      Gson gson = new GsonBuilder()
        .registerTypeAdapter(Base.class, new JsonSerializer<Base>() {
+         @Override
          public JsonElement serialize(Base src, Type typeOfSrc, JsonSerializationContext context) {
            return null;
          }
diff --git a/gson/src/test/java/com/google/gson/functional/CustomTypeAdaptersTest.java b/gson/src/test/java/com/google/gson/functional/CustomTypeAdaptersTest.java
index b452849dd9..219d7db665 100644
--- a/gson/src/test/java/com/google/gson/functional/CustomTypeAdaptersTest.java
+++ b/gson/src/test/java/com/google/gson/functional/CustomTypeAdaptersTest.java
@@ -15,6 +15,11 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.InstanceCreator;
@@ -29,15 +34,15 @@
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.common.TestTypes.ClassWithCustomTypeConverter;
 import com.google.gson.reflect.TypeToken;
-
-import java.util.Date;
-import junit.framework.TestCase;
-
 import java.lang.reflect.Type;
+import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the support of custom serializer and deserializers.
@@ -45,16 +50,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class CustomTypeAdaptersTest extends TestCase {
+class CustomTypeAdaptersTest {
   private GsonBuilder builder;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     builder = new GsonBuilder();
   }
 
-  public void testCustomSerializers() {
+  @Test
+  void testCustomSerializers() {
     Gson gson = builder.registerTypeAdapter(
         ClassWithCustomTypeConverter.class, new JsonSerializer<ClassWithCustomTypeConverter>() {
           @Override public JsonElement serialize(ClassWithCustomTypeConverter src, Type typeOfSrc,
@@ -69,7 +74,8 @@ public void testCustomSerializers() {
     assertEquals("{\"bag\":5,\"value\":25}", gson.toJson(target));
   }
 
-  public void testCustomDeserializers() {
+  @Test
+  void testCustomDeserializers() {
     Gson gson = new GsonBuilder().registerTypeAdapter(
         ClassWithCustomTypeConverter.class, new JsonDeserializer<ClassWithCustomTypeConverter>() {
           @Override public ClassWithCustomTypeConverter deserialize(JsonElement json, Type typeOfT,
@@ -85,7 +91,9 @@ public void testCustomDeserializers() {
     assertEquals(5, target.getBag().getIntValue());
   }
 
-  public void disable_testCustomSerializersOfSelf() {
+  @Disabled
+  @Test
+  void testCustomSerializersOfSelf() {
     Gson gson = createGsonObjectWithFooTypeAdapter();
     Gson basicGson = new Gson();
     Foo newFooObject = new Foo(1, 2L);
@@ -95,7 +103,9 @@ public void disable_testCustomSerializersOfSelf() {
     assertEquals(jsonFromGson, jsonFromCustomSerializer);
   }
 
-  public void disable_testCustomDeserializersOfSelf() {
+  @Disabled
+  @Test
+  void testCustomDeserializersOfSelf() {
     Gson gson = createGsonObjectWithFooTypeAdapter();
     Gson basicGson = new Gson();
     Foo expectedFoo = new Foo(1, 2L);
@@ -106,7 +116,8 @@ public void disable_testCustomDeserializersOfSelf() {
     assertEquals(expectedFoo.value, newFooObject.value);
   }
 
-  public void testCustomNestedSerializers() {
+  @Test
+  void testCustomNestedSerializers() {
     Gson gson = new GsonBuilder().registerTypeAdapter(
         BagOfPrimitives.class, new JsonSerializer<BagOfPrimitives>() {
           @Override public JsonElement serialize(BagOfPrimitives src, Type typeOfSrc,
@@ -118,7 +129,8 @@ public void testCustomNestedSerializers() {
     assertEquals("{\"bag\":6,\"value\":10}", gson.toJson(target));
   }
 
-  public void testCustomNestedDeserializers() {
+  @Test
+  void testCustomNestedDeserializers() {
     Gson gson = new GsonBuilder().registerTypeAdapter(
         BagOfPrimitives.class, new JsonDeserializer<BagOfPrimitives>() {
           @Override public BagOfPrimitives deserialize(JsonElement json, Type typeOfT,
@@ -132,7 +144,8 @@ public void testCustomNestedDeserializers() {
     assertEquals(7, target.getBag().getIntValue());
   }
 
-  public void testCustomTypeAdapterDoesNotAppliesToSubClasses() {
+  @Test
+  void testCustomTypeAdapterDoesNotAppliesToSubClasses() {
     Gson gson = new GsonBuilder().registerTypeAdapter(Base.class, new JsonSerializer<Base> () {
       @Override
       public JsonElement serialize(Base src, Type typeOfSrc, JsonSerializationContext context) {
@@ -149,7 +162,8 @@ public JsonElement serialize(Base src, Type typeOfSrc, JsonSerializationContext
     assertTrue(json.contains("derivedValue"));
   }
 
-  public void testCustomTypeAdapterAppliesToSubClassesSerializedAsBaseClass() {
+  @Test
+  void testCustomTypeAdapterAppliesToSubClassesSerializedAsBaseClass() {
     Gson gson = new GsonBuilder().registerTypeAdapter(Base.class, new JsonSerializer<Base> () {
       @Override
       public JsonElement serialize(Base src, Type typeOfSrc, JsonSerializationContext context) {
@@ -181,7 +195,7 @@ private Gson createGsonObjectWithFooTypeAdapter() {
     return new GsonBuilder().registerTypeAdapter(Foo.class, new FooTypeAdapter()).create();
   }
 
-  public static class Foo {
+  static class Foo {
     private final int key;
     private final long value;
 
@@ -195,7 +209,7 @@ public Foo(int key, long value) {
     }
   }
 
-  public static final class FooTypeAdapter implements JsonSerializer<Foo>, JsonDeserializer<Foo> {
+  static final class FooTypeAdapter implements JsonSerializer<Foo>, JsonDeserializer<Foo> {
     @Override
     public Foo deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
         throws JsonParseException {
@@ -208,7 +222,8 @@ public JsonElement serialize(Foo src, Type typeOfSrc, JsonSerializationContext c
     }
   }
 
-  public void testCustomSerializerInvokedForPrimitives() {
+  @Test
+  void testCustomSerializerInvokedForPrimitives() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(boolean.class, new JsonSerializer<Boolean>() {
           @Override public JsonElement serialize(Boolean s, Type t, JsonSerializationContext c) {
@@ -220,12 +235,12 @@ public void testCustomSerializerInvokedForPrimitives() {
     assertEquals("true", gson.toJson(true, Boolean.class));
   }
 
-  @SuppressWarnings("rawtypes")
-  public void testCustomDeserializerInvokedForPrimitives() {
+  @Test
+  void testCustomDeserializerInvokedForPrimitives() {
     Gson gson = new GsonBuilder()
-        .registerTypeAdapter(boolean.class, new JsonDeserializer() {
+        .registerTypeAdapter(boolean.class, new JsonDeserializer<Boolean>() {
           @Override
-          public Object deserialize(JsonElement json, Type t, JsonDeserializationContext context) {
+          public Boolean deserialize(JsonElement json, Type t, JsonDeserializationContext context) {
             return json.getAsInt() != 0;
           }
         })
@@ -234,7 +249,8 @@ public Object deserialize(JsonElement json, Type t, JsonDeserializationContext c
     assertEquals(Boolean.TRUE, gson.fromJson("true", Boolean.class));
   }
 
-  public void testCustomByteArraySerializer() {
+  @Test
+  void testCustomByteArraySerializer() {
     Gson gson = new GsonBuilder().registerTypeAdapter(byte[].class, new JsonSerializer<byte[]>() {
       @Override
       public JsonElement serialize(byte[] src, Type typeOfSrc, JsonSerializationContext context) {
@@ -250,7 +266,8 @@ public JsonElement serialize(byte[] src, Type typeOfSrc, JsonSerializationContex
     assertEquals("\"0123456789\"", json);
   }
 
-  public void testCustomByteArrayDeserializerAndInstanceCreator() {
+  @Test
+  void testCustomByteArrayDeserializerAndInstanceCreator() {
     GsonBuilder gsonBuilder = new GsonBuilder().registerTypeAdapter(byte[].class,
         new JsonDeserializer<byte[]>() {
           @Override public byte[] deserialize(JsonElement json,
@@ -308,7 +325,8 @@ private static class StringHolderTypeAdapter implements JsonSerializer<StringHol
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForCollectionElementSerializationWithType() {
+  @Test
+  void testCustomAdapterInvokedForCollectionElementSerializationWithType() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -321,7 +339,8 @@ public void testCustomAdapterInvokedForCollectionElementSerializationWithType()
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForCollectionElementSerialization() {
+  @Test
+  void testCustomAdapterInvokedForCollectionElementSerialization() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -333,7 +352,8 @@ public void testCustomAdapterInvokedForCollectionElementSerialization() {
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForCollectionElementDeserialization() {
+  @Test
+  void testCustomAdapterInvokedForCollectionElementDeserialization() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -346,7 +366,8 @@ public void testCustomAdapterInvokedForCollectionElementDeserialization() {
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForMapElementSerializationWithType() {
+  @Test
+  void testCustomAdapterInvokedForMapElementSerializationWithType() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -359,7 +380,8 @@ public void testCustomAdapterInvokedForMapElementSerializationWithType() {
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForMapElementSerialization() {
+  @Test
+  void testCustomAdapterInvokedForMapElementSerialization() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -371,7 +393,8 @@ public void testCustomAdapterInvokedForMapElementSerialization() {
   }
 
   // Test created from Issue 70
-  public void testCustomAdapterInvokedForMapElementDeserialization() {
+  @Test
+  void testCustomAdapterInvokedForMapElementDeserialization() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(StringHolder.class, new StringHolderTypeAdapter())
       .create();
@@ -383,7 +406,8 @@ public void testCustomAdapterInvokedForMapElementDeserialization() {
     assertEquals("Tomaw", foo.part2);
   }
 
-  public void testEnsureCustomSerializerNotInvokedForNullValues() {
+  @Test
+  void testEnsureCustomSerializerNotInvokedForNullValues() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(DataHolder.class, new DataHolderSerializer())
         .create();
@@ -392,7 +416,8 @@ public void testEnsureCustomSerializerNotInvokedForNullValues() {
     assertEquals("{\"wrappedData\":{\"myData\":\"abc\"}}", json);
   }
 
-  public void testEnsureCustomDeserializerNotInvokedForNullValues() {
+  @Test
+  void testEnsureCustomDeserializerNotInvokedForNullValues() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(DataHolder.class, new DataHolderDeserializer())
         .create();
@@ -402,7 +427,8 @@ public void testEnsureCustomDeserializerNotInvokedForNullValues() {
   }
 
   // Test created from Issue 352
-  public void testRegisterHierarchyAdapterForDate() {
+  @Test
+  void testRegisterHierarchyAdapterForDate() {
     Gson gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Date.class, new DateTypeAdapter())
         .create();
diff --git a/gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java b/gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java
index 1f9c75cd49..c205aee418 100644
--- a/gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java
+++ b/gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java
@@ -15,6 +15,11 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonArray;
@@ -54,8 +59,9 @@
 import java.util.TimeZone;
 import java.util.TreeSet;
 import java.util.UUID;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional test for Json serialization and deserialization for common classes for which default
@@ -64,14 +70,13 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class DefaultTypeAdaptersTest extends TestCase {
+public class DefaultTypeAdaptersTest {
   private Gson gson;
   private TimeZone oldTimeZone;
   private Locale oldLocale;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     this.oldTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
     this.oldLocale = Locale.getDefault();
@@ -79,14 +84,14 @@ protected void setUp() throws Exception {
     gson = new Gson();
   }
 
-  @Override
-  protected void tearDown() throws Exception {
+  @AfterEach
+  void tearDown() throws Exception {
     TimeZone.setDefault(oldTimeZone);
     Locale.setDefault(oldLocale);
-    super.tearDown();
   }
 
-  public void testClassSerialization() {
+  @Test
+  void testClassSerialization() {
     try {
       gson.toJson(String.class);
       fail();
@@ -97,7 +102,8 @@ public void testClassSerialization() {
     assertEquals("\"java.lang.String\"", gson.toJson(String.class));
   }
 
-  public void testClassDeserialization() {
+  @Test
+  void testClassDeserialization() {
     try {
       gson.fromJson("String.class", String.class.getClass());
       fail();
@@ -108,13 +114,15 @@ public void testClassDeserialization() {
     assertEquals(String.class, gson.fromJson("java.lang.String", Class.class));
   }
 
-  public void testUrlSerialization() throws Exception {
+  @Test
+  void testUrlSerialization() throws Exception {
     String urlValue = "http://google.com/";
     URL url = new URL(urlValue);
     assertEquals("\"http://google.com/\"", gson.toJson(url));
   }
 
-  public void testUrlDeserialization() {
+  @Test
+  void testUrlDeserialization() {
     String urlValue = "http://google.com/";
     String json = "'http:\\/\\/google.com\\/'";
     URL target = gson.fromJson(json, URL.class);
@@ -124,12 +132,14 @@ public void testUrlDeserialization() {
     assertEquals(urlValue, target.toExternalForm());
   }
 
-  public void testUrlNullSerialization() throws Exception {
+  @Test
+  void testUrlNullSerialization() throws Exception {
     ClassWithUrlField target = new ClassWithUrlField();
     assertEquals("{}", gson.toJson(target));
   }
 
-  public void testUrlNullDeserialization() {
+  @Test
+  void testUrlNullDeserialization() {
     String json = "{}";
     ClassWithUrlField target = gson.fromJson(json, ClassWithUrlField.class);
     assertNull(target.url);
@@ -139,20 +149,23 @@ private static class ClassWithUrlField {
     URL url;
   }
 
-  public void testUriSerialization() throws Exception {
+  @Test
+  void testUriSerialization() throws Exception {
     String uriValue = "http://google.com/";
     URI uri = new URI(uriValue);
     assertEquals("\"http://google.com/\"", gson.toJson(uri));
   }
 
-  public void testUriDeserialization() {
+  @Test
+  void testUriDeserialization() {
     String uriValue = "http://google.com/";
     String json = '"' + uriValue + '"';
     URI target = gson.fromJson(json, URI.class);
     assertEquals(uriValue, target.toASCIIString());
   }
 
-  public void testNullSerialization() throws Exception {
+  @Test
+  void testNullSerialization() throws Exception {
     testNullSerializationAndDeserialization(Boolean.class);
     testNullSerializationAndDeserialization(Byte.class);
     testNullSerializationAndDeserialization(Short.class);
@@ -192,48 +205,56 @@ public static void testNullSerializationAndDeserialization(Gson gson, Class<?> c
     assertEquals(null, gson.fromJson("null", c));
   }
 
-  public void testUuidSerialization() throws Exception {
+  @Test
+  void testUuidSerialization() throws Exception {
     String uuidValue = "c237bec1-19ef-4858-a98e-521cf0aad4c0";
     UUID uuid = UUID.fromString(uuidValue);
     assertEquals('"' + uuidValue + '"', gson.toJson(uuid));
   }
 
-  public void testUuidDeserialization() {
+  @Test
+  void testUuidDeserialization() {
     String uuidValue = "c237bec1-19ef-4858-a98e-521cf0aad4c0";
     String json = '"' + uuidValue + '"';
     UUID target = gson.fromJson(json, UUID.class);
     assertEquals(uuidValue, target.toString());
   }
 
-  public void testLocaleSerializationWithLanguage() {
+  @Test
+  void testLocaleSerializationWithLanguage() {
     Locale target = new Locale("en");
     assertEquals("\"en\"", gson.toJson(target));
   }
 
-  public void testLocaleDeserializationWithLanguage() {
+  @Test
+  void testLocaleDeserializationWithLanguage() {
     String json = "\"en\"";
     Locale locale = gson.fromJson(json, Locale.class);
     assertEquals("en", locale.getLanguage());
   }
 
-  public void testLocaleSerializationWithLanguageCountry() {
+  @Test
+  void testLocaleSerializationWithLanguageCountry() {
     Locale target = Locale.CANADA_FRENCH;
     assertEquals("\"fr_CA\"", gson.toJson(target));
   }
 
-  public void testLocaleDeserializationWithLanguageCountry() {
+  @Test
+  void testLocaleDeserializationWithLanguageCountry() {
     String json = "\"fr_CA\"";
     Locale locale = gson.fromJson(json, Locale.class);
     assertEquals(Locale.CANADA_FRENCH, locale);
   }
 
-  public void testLocaleSerializationWithLanguageCountryVariant() {
+  @Test
+  void testLocaleSerializationWithLanguageCountryVariant() {
     Locale target = new Locale("de", "DE", "EURO");
     String json = gson.toJson(target);
     assertEquals("\"de_DE_EURO\"", json);
   }
 
-  public void testLocaleDeserializationWithLanguageCountryVariant() {
+  @Test
+  void testLocaleDeserializationWithLanguageCountryVariant() {
     String json = "\"de_DE_EURO\"";
     Locale locale = gson.fromJson(json, Locale.class);
     assertEquals("de", locale.getLanguage());
@@ -241,41 +262,47 @@ public void testLocaleDeserializationWithLanguageCountryVariant() {
     assertEquals("EURO", locale.getVariant());
   }
 
-  public void testBigDecimalFieldSerialization() {
+  @Test
+  void testBigDecimalFieldSerialization() {
     ClassWithBigDecimal target = new ClassWithBigDecimal("-122.01e-21");
     String json = gson.toJson(target);
     String actual = json.substring(json.indexOf(':') + 1, json.indexOf('}'));
     assertEquals(target.value, new BigDecimal(actual));
   }
 
-  public void testBigDecimalFieldDeserialization() {
+  @Test
+  void testBigDecimalFieldDeserialization() {
     ClassWithBigDecimal expected = new ClassWithBigDecimal("-122.01e-21");
     String json = expected.getExpectedJson();
     ClassWithBigDecimal actual = gson.fromJson(json, ClassWithBigDecimal.class);
     assertEquals(expected.value, actual.value);
   }
 
-  public void testBadValueForBigDecimalDeserialization() {
+  @Test
+  void testBadValueForBigDecimalDeserialization() {
     try {
       gson.fromJson("{\"value\"=1.5e-1.0031}", ClassWithBigDecimal.class);
       fail("Exponent of a BigDecimal must be an integer value.");
     } catch (JsonParseException expected) { }
   }
 
-  public void testBigIntegerFieldSerialization() {
+  @Test
+  void testBigIntegerFieldSerialization() {
     ClassWithBigInteger target = new ClassWithBigInteger("23232323215323234234324324324324324324");
     String json = gson.toJson(target);
     assertEquals(target.getExpectedJson(), json);
   }
 
-  public void testBigIntegerFieldDeserialization() {
+  @Test
+  void testBigIntegerFieldDeserialization() {
     ClassWithBigInteger expected = new ClassWithBigInteger("879697697697697697697697697697697697");
     String json = expected.getExpectedJson();
     ClassWithBigInteger actual = gson.fromJson(json, ClassWithBigInteger.class);
     assertEquals(expected.value, actual.value);
   }
 
-  public void testOverrideBigIntegerTypeAdapter() throws Exception {
+  @Test
+  void testOverrideBigIntegerTypeAdapter() throws Exception {
     gson = new GsonBuilder()
         .registerTypeAdapter(BigInteger.class, new NumberAsStringAdapter(BigInteger.class))
         .create();
@@ -283,7 +310,8 @@ public void testOverrideBigIntegerTypeAdapter() throws Exception {
     assertEquals(new BigInteger("123"), gson.fromJson("\"123\"", BigInteger.class));
   }
 
-  public void testOverrideBigDecimalTypeAdapter() throws Exception {
+  @Test
+  void testOverrideBigDecimalTypeAdapter() throws Exception {
     gson = new GsonBuilder()
         .registerTypeAdapter(BigDecimal.class, new NumberAsStringAdapter(BigDecimal.class))
         .create();
@@ -291,7 +319,8 @@ public void testOverrideBigDecimalTypeAdapter() throws Exception {
     assertEquals(new BigDecimal("1.1"), gson.fromJson("\"1.1\"", BigDecimal.class));
   }
 
-  public void testSetSerialization() throws Exception {
+  @Test
+  void testSetSerialization() throws Exception {
     Gson gson = new Gson();
     HashSet<String> s = new HashSet<String>();
     s.add("blah");
@@ -302,7 +331,8 @@ public void testSetSerialization() throws Exception {
     assertEquals("[\"blah\"]", json);
   }
 
-  public void testBitSetSerialization() throws Exception {
+  @Test
+  void testBitSetSerialization() throws Exception {
     Gson gson = new Gson();
     BitSet bits = new BitSet();
     bits.set(1);
@@ -312,7 +342,8 @@ public void testBitSetSerialization() throws Exception {
     assertEquals("[0,1,0,1,1,1,0,0,0,1]", json);
   }
 
-  public void testBitSetDeserialization() throws Exception {
+  @Test
+  void testBitSetDeserialization() throws Exception {
     BitSet expected = new BitSet();
     expected.set(0);
     expected.set(2, 6);
@@ -346,7 +377,8 @@ public void testBitSetDeserialization() throws Exception {
     }
   }
 
-  public void testDefaultDateSerialization() {
+  @Test
+  void testDefaultDateSerialization() {
     Date now = new Date(1315806903103L);
     String json = gson.toJson(now);
     if (JavaVersion.isJava9OrLater()) {
@@ -356,7 +388,8 @@ public void testDefaultDateSerialization() {
     }
   }
 
-  public void testDefaultDateDeserialization() {
+  @Test
+  void testDefaultDateDeserialization() {
     String json = "'Dec 13, 2009 07:18:02 AM'";
     Date extracted = gson.fromJson(json, Date.class);
     assertEqualsDate(extracted, 2009, 11, 13);
@@ -379,7 +412,8 @@ public static void assertEqualsTime(Date date, int hours, int minutes, int secon
     assertEquals(seconds, date.getSeconds());
   }
 
-  public void testDefaultDateSerializationUsingBuilder() throws Exception {
+  @Test
+  void testDefaultDateSerializationUsingBuilder() throws Exception {
     Gson gson = new GsonBuilder().create();
     Date now = new Date(1315806903103L);
     String json = gson.toJson(now);
@@ -390,7 +424,8 @@ public void testDefaultDateSerializationUsingBuilder() throws Exception {
     }
   }
 
-  public void testDefaultDateDeserializationUsingBuilder() throws Exception {
+  @Test
+  void testDefaultDateDeserializationUsingBuilder() throws Exception {
     Gson gson = new GsonBuilder().create();
     Date now = new Date(1315806903103L);
     String json = gson.toJson(now);
@@ -398,7 +433,8 @@ public void testDefaultDateDeserializationUsingBuilder() throws Exception {
     assertEquals(now.toString(), extracted.toString());
   }
 
-  public void testDefaultCalendarSerialization() throws Exception {
+  @Test
+  void testDefaultCalendarSerialization() throws Exception {
     Gson gson = new GsonBuilder().create();
     String json = gson.toJson(Calendar.getInstance());
     assertTrue(json.contains("year"));
@@ -409,7 +445,8 @@ public void testDefaultCalendarSerialization() throws Exception {
     assertTrue(json.contains("second"));
   }
 
-  public void testDefaultCalendarDeserialization() throws Exception {
+  @Test
+  void testDefaultCalendarDeserialization() throws Exception {
     Gson gson = new GsonBuilder().create();
     String json = "{year:2009,month:2,dayOfMonth:11,hourOfDay:14,minute:29,second:23}";
     Calendar cal = gson.fromJson(json, Calendar.class);
@@ -421,7 +458,8 @@ public void testDefaultCalendarDeserialization() throws Exception {
     assertEquals(23, cal.get(Calendar.SECOND));
   }
 
-  public void testDefaultGregorianCalendarSerialization() throws Exception {
+  @Test
+  void testDefaultGregorianCalendarSerialization() throws Exception {
     Gson gson = new GsonBuilder().create();
     GregorianCalendar cal = new GregorianCalendar();
     String json = gson.toJson(cal);
@@ -433,7 +471,8 @@ public void testDefaultGregorianCalendarSerialization() throws Exception {
     assertTrue(json.contains("second"));
   }
 
-  public void testDefaultGregorianCalendarDeserialization() throws Exception {
+  @Test
+  void testDefaultGregorianCalendarDeserialization() throws Exception {
     Gson gson = new GsonBuilder().create();
     String json = "{year:2009,month:2,dayOfMonth:11,hourOfDay:14,minute:29,second:23}";
     GregorianCalendar cal = gson.fromJson(json, GregorianCalendar.class);
@@ -445,7 +484,8 @@ public void testDefaultGregorianCalendarDeserialization() throws Exception {
     assertEquals(23, cal.get(Calendar.SECOND));
   }
 
-  public void testDateSerializationWithPattern() throws Exception {
+  @Test
+  void testDateSerializationWithPattern() throws Exception {
     String pattern = "yyyy-MM-dd";
     Gson gson = new GsonBuilder().setDateFormat(DateFormat.FULL).setDateFormat(pattern).create();
     Date now = new Date(1315806903103L);
@@ -454,7 +494,8 @@ public void testDateSerializationWithPattern() throws Exception {
   }
 
   @SuppressWarnings("deprecation")
-  public void testDateDeserializationWithPattern() throws Exception {
+  @Test
+  void testDateDeserializationWithPattern() throws Exception {
     String pattern = "yyyy-MM-dd";
     Gson gson = new GsonBuilder().setDateFormat(DateFormat.FULL).setDateFormat(pattern).create();
     Date now = new Date(1315806903103L);
@@ -465,11 +506,13 @@ public void testDateDeserializationWithPattern() throws Exception {
     assertEquals(now.getDay(), extracted.getDay());
   }
 
-  public void testDateSerializationWithPatternNotOverridenByTypeAdapter() throws Exception {
+  @Test
+  void testDateSerializationWithPatternNotOverridenByTypeAdapter() throws Exception {
     String pattern = "yyyy-MM-dd";
     Gson gson = new GsonBuilder()
         .setDateFormat(pattern)
         .registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
+          @Override
           public Date deserialize(JsonElement json, Type typeOfT,
               JsonDeserializationContext context)
               throws JsonParseException {
@@ -484,7 +527,8 @@ public Date deserialize(JsonElement json, Type typeOfT,
   }
 
   // http://code.google.com/p/google-gson/issues/detail?id=230
-  public void testDateSerializationInCollection() throws Exception {
+  @Test
+  void testDateSerializationInCollection() throws Exception {
     Type listOfDates = new TypeToken<List<Date>>() {}.getType();
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
@@ -502,14 +546,16 @@ public void testDateSerializationInCollection() throws Exception {
     }
   }
 
-  public void testJsonPrimitiveSerialization() {
+  @Test
+  void testJsonPrimitiveSerialization() {
     assertEquals("5", gson.toJson(new JsonPrimitive(5), JsonElement.class));
     assertEquals("true", gson.toJson(new JsonPrimitive(true), JsonElement.class));
     assertEquals("\"foo\"", gson.toJson(new JsonPrimitive("foo"), JsonElement.class));
     assertEquals("\"a\"", gson.toJson(new JsonPrimitive('a'), JsonElement.class));
   }
 
-  public void testJsonPrimitiveDeserialization() {
+  @Test
+  void testJsonPrimitiveDeserialization() {
     assertEquals(new JsonPrimitive(5), gson.fromJson("5", JsonElement.class));
     assertEquals(new JsonPrimitive(5), gson.fromJson("5", JsonPrimitive.class));
     assertEquals(new JsonPrimitive(true), gson.fromJson("true", JsonElement.class));
@@ -520,17 +566,20 @@ public void testJsonPrimitiveDeserialization() {
     assertEquals(new JsonPrimitive('a'), gson.fromJson("\"a\"", JsonPrimitive.class));
   }
 
-  public void testJsonNullSerialization() {
+  @Test
+  void testJsonNullSerialization() {
     assertEquals("null", gson.toJson(JsonNull.INSTANCE, JsonElement.class));
     assertEquals("null", gson.toJson(JsonNull.INSTANCE, JsonNull.class));
   }
 
-  public void testNullJsonElementSerialization() {
+  @Test
+  void testNullJsonElementSerialization() {
     assertEquals("null", gson.toJson(null, JsonElement.class));
     assertEquals("null", gson.toJson(null, JsonNull.class));
   }
 
-  public void testJsonArraySerialization() {
+  @Test
+  void testJsonArraySerialization() {
     JsonArray array = new JsonArray();
     array.add(new JsonPrimitive(1));
     array.add(new JsonPrimitive(2));
@@ -538,7 +587,8 @@ public void testJsonArraySerialization() {
     assertEquals("[1,2,3]", gson.toJson(array, JsonElement.class));
   }
 
-  public void testJsonArrayDeserialization() {
+  @Test
+  void testJsonArrayDeserialization() {
     JsonArray array = new JsonArray();
     array.add(new JsonPrimitive(1));
     array.add(new JsonPrimitive(2));
@@ -549,14 +599,16 @@ public void testJsonArrayDeserialization() {
     assertEquals(array, gson.fromJson(json, JsonArray.class));
   }
 
-  public void testJsonObjectSerialization() {
+  @Test
+  void testJsonObjectSerialization() {
     JsonObject object = new JsonObject();
     object.add("foo", new JsonPrimitive(1));
     object.add("bar", new JsonPrimitive(2));
     assertEquals("{\"foo\":1,\"bar\":2}", gson.toJson(object, JsonElement.class));
   }
 
-  public void testJsonObjectDeserialization() {
+  @Test
+  void testJsonObjectDeserialization() {
     JsonObject object = new JsonObject();
     object.add("foo", new JsonPrimitive(1));
     object.add("bar", new JsonPrimitive(2));
@@ -569,12 +621,14 @@ public void testJsonObjectDeserialization() {
     assertEquals(object, actualObj);
   }
 
-  public void testJsonNullDeserialization() {
+  @Test
+  void testJsonNullDeserialization() {
     assertEquals(JsonNull.INSTANCE, gson.fromJson("null", JsonElement.class));
     assertEquals(JsonNull.INSTANCE, gson.fromJson("null", JsonNull.class));
   }
 
-  public void testJsonElementTypeMismatch() {
+  @Test
+  void testJsonElementTypeMismatch() {
     try {
       gson.fromJson("\"abc\"", JsonObject.class);
       fail();
@@ -604,7 +658,8 @@ String getExpectedJson() {
     }
   }
 
-  public void testPropertiesSerialization() {
+  @Test
+  void testPropertiesSerialization() {
     Properties props = new Properties();
     props.setProperty("foo", "bar");
     String json = gson.toJson(props);
@@ -612,44 +667,51 @@ public void testPropertiesSerialization() {
     assertEquals(expected, json);
   }
 
-  public void testPropertiesDeserialization() {
+  @Test
+  void testPropertiesDeserialization() {
     String json = "{foo:'bar'}";
     Properties props = gson.fromJson(json, Properties.class);
     assertEquals("bar", props.getProperty("foo"));
   }
 
-  public void testTreeSetSerialization() {
+  @Test
+  void testTreeSetSerialization() {
     TreeSet<String> treeSet = new TreeSet<String>();
     treeSet.add("Value1");
     String json = gson.toJson(treeSet);
     assertEquals("[\"Value1\"]", json);
   }
 
-  public void testTreeSetDeserialization() {
+  @Test
+  void testTreeSetDeserialization() {
     String json = "['Value1']";
     Type type = new TypeToken<TreeSet<String>>() {}.getType();
     TreeSet<String> treeSet = gson.fromJson(json, type);
     assertTrue(treeSet.contains("Value1"));
   }
 
-  public void testStringBuilderSerialization() {
+  @Test
+  void testStringBuilderSerialization() {
     StringBuilder sb = new StringBuilder("abc");
     String json = gson.toJson(sb);
     assertEquals("\"abc\"", json);
   }
 
-  public void testStringBuilderDeserialization() {
+  @Test
+  void testStringBuilderDeserialization() {
     StringBuilder sb = gson.fromJson("'abc'", StringBuilder.class);
     assertEquals("abc", sb.toString());
   }
 
-  public void testStringBufferSerialization() {
+  @Test
+  void testStringBufferSerialization() {
     StringBuffer sb = new StringBuffer("abc");
     String json = gson.toJson(sb);
     assertEquals("\"abc\"", json);
   }
 
-  public void testStringBufferDeserialization() {
+  @Test
+  void testStringBufferDeserialization() {
     StringBuffer sb = gson.fromJson("'abc'", StringBuffer.class);
     assertEquals("abc", sb.toString());
   }
diff --git a/gson/src/test/java/com/google/gson/functional/DelegateTypeAdapterTest.java b/gson/src/test/java/com/google/gson/functional/DelegateTypeAdapterTest.java
index f89148e364..941f7afab4 100644
--- a/gson/src/test/java/com/google/gson/functional/DelegateTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/functional/DelegateTypeAdapterTest.java
@@ -15,11 +15,7 @@
  */
 package com.google.gson.functional;
 
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.List;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -29,27 +25,32 @@
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for {@link Gson#getDelegateAdapter(TypeAdapterFactory, TypeToken)} method.
  *
  * @author Inderjeet Singh
  */
-public class DelegateTypeAdapterTest extends TestCase {
+class DelegateTypeAdapterTest {
 
   private StatsTypeAdapterFactory stats;
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     stats = new StatsTypeAdapterFactory();
     gson = new GsonBuilder()
       .registerTypeAdapterFactory(stats)
       .create();
   }
 
-  public void testDelegateInvoked() {
+  @Test
+  void testDelegateInvoked() {
     List<BagOfPrimitives> bags = new ArrayList<BagOfPrimitives>();
     for (int i = 0; i < 10; ++i) {
       bags.add(new BagOfPrimitives(i, i, i % 2 == 0, String.valueOf(i)));
@@ -61,7 +62,8 @@ public void testDelegateInvoked() {
     assertEquals(51, stats.numWrites);
   }
 
-  public void testDelegateInvokedOnStrings() {
+  @Test
+  void testDelegateInvokedOnStrings() {
     String[] bags = {"1", "2", "3", "4"};
     String json = gson.toJson(bags);
     bags = gson.fromJson(json, String[].class);
diff --git a/gson/src/test/java/com/google/gson/functional/EnumTest.java b/gson/src/test/java/com/google/gson/functional/EnumTest.java
index 8a1c6e12c6..37d2b9ba70 100644
--- a/gson/src/test/java/com/google/gson/functional/EnumTest.java
+++ b/gson/src/test/java/com/google/gson/functional/EnumTest.java
@@ -16,6 +16,10 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -33,34 +37,38 @@
 import java.util.Collection;
 import java.util.EnumSet;
 import java.util.Set;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
 /**
  * Functional tests for Java 5.0 enums.
  *
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class EnumTest extends TestCase {
+class EnumTest {
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testTopLevelEnumSerialization() throws Exception {
+  @Test
+  void testTopLevelEnumSerialization() throws Exception {
     String result = gson.toJson(MyEnum.VALUE1);
     assertEquals('"' + MyEnum.VALUE1.toString() + '"', result);
   }
 
-  public void testTopLevelEnumDeserialization() throws Exception {
+  @Test
+  void testTopLevelEnumDeserialization() throws Exception {
     MyEnum result = gson.fromJson('"' + MyEnum.VALUE1.toString() + '"', MyEnum.class);
     assertEquals(MyEnum.VALUE1, result);
   }
 
-  public void testCollectionOfEnumsSerialization() {
+  @Test
+  void testCollectionOfEnumsSerialization() {
     Type type = new TypeToken<Collection<MyEnum>>() {}.getType();
     Collection<MyEnum> target = new ArrayList<MyEnum>();
     target.add(MyEnum.VALUE1);
@@ -72,7 +80,8 @@ public void testCollectionOfEnumsSerialization() {
     assertEquals(expectedJson, actualJson);
   }
 
-  public void testCollectionOfEnumsDeserialization() {
+  @Test
+  void testCollectionOfEnumsDeserialization() {
     Type type = new TypeToken<Collection<MyEnum>>() {}.getType();
     String json = "[\"VALUE1\",\"VALUE2\"]";
     Collection<MyEnum> target = gson.fromJson(json, type);
@@ -80,12 +89,14 @@ public void testCollectionOfEnumsDeserialization() {
     MoreAsserts.assertContains(target, MyEnum.VALUE2);
   }
 
-  public void testClassWithEnumFieldSerialization() throws Exception {
+  @Test
+  void testClassWithEnumFieldSerialization() throws Exception {
     ClassWithEnumFields target = new ClassWithEnumFields();
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testClassWithEnumFieldDeserialization() throws Exception {
+  @Test
+  void testClassWithEnumFieldDeserialization() throws Exception {
     String json = "{value1:'VALUE1',value2:'VALUE2'}";
     ClassWithEnumFields target = gson.fromJson(json, ClassWithEnumFields.class);
     assertEquals(MyEnum.VALUE1,target.value1);
@@ -107,7 +118,8 @@ public String getExpectedJson() {
   /**
    * Test for issue 226.
    */
-  public void testEnumSubclass() {
+  @Test
+  void testEnumSubclass() {
     assertFalse(Roshambo.class == Roshambo.ROCK.getClass());
     assertEquals("\"ROCK\"", gson.toJson(Roshambo.ROCK));
     assertEquals("[\"ROCK\",\"PAPER\",\"SCISSORS\"]", gson.toJson(EnumSet.allOf(Roshambo.class)));
@@ -116,7 +128,8 @@ public void testEnumSubclass() {
         gson.fromJson("[\"ROCK\",\"PAPER\",\"SCISSORS\"]", new TypeToken<Set<Roshambo>>() {}.getType()));
   }
 
-  public void testEnumSubclassWithRegisteredTypeAdapter() {
+  @Test
+  void testEnumSubclassWithRegisteredTypeAdapter() {
     gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Roshambo.class, new MyEnumTypeAdapter())
         .create();
@@ -128,7 +141,8 @@ public void testEnumSubclassWithRegisteredTypeAdapter() {
         gson.fromJson("[\"123ROCK\",\"123PAPER\",\"123SCISSORS\"]", new TypeToken<Set<Roshambo>>() {}.getType()));
   }
 
-  public void testEnumSubclassAsParameterizedType() {
+  @Test
+  void testEnumSubclassAsParameterizedType() {
     Collection<Roshambo> list = new ArrayList<Roshambo>();
     list.add(Roshambo.ROCK);
     list.add(Roshambo.PAPER);
@@ -142,12 +156,14 @@ public void testEnumSubclassAsParameterizedType() {
     MoreAsserts.assertContains(actualJsonList, Roshambo.PAPER);
   }
 
-  public void testEnumCaseMapping() {
+  @Test
+  void testEnumCaseMapping() {
     assertEquals(Gender.MALE, gson.fromJson("\"boy\"", Gender.class));
     assertEquals("\"boy\"", gson.toJson(Gender.MALE, Gender.class));
   }
 
-  public void testEnumSet() {
+  @Test
+  void testEnumSet() {
     EnumSet<Roshambo> foo = EnumSet.of(Roshambo.ROCK, Roshambo.PAPER);
     String json = gson.toJson(foo);
     Type type = new TypeToken<EnumSet<Roshambo>>() {}.getType();
@@ -157,7 +173,7 @@ public void testEnumSet() {
     assertFalse(bar.contains(Roshambo.SCISSORS));
   }
 
-  public enum Roshambo {
+  enum Roshambo {
     ROCK {
       @Override Roshambo defeats() {
         return SCISSORS;
@@ -189,7 +205,7 @@ private static class MyEnumTypeAdapter
     }
   }
 
-  public enum Gender {
+  enum Gender {
     @SerializedName("boy")
     MALE,
 
@@ -197,12 +213,13 @@ public enum Gender {
     FEMALE
   }
 
-  public void testEnumClassWithFields() {
+  @Test
+  void testEnumClassWithFields() {
     assertEquals("\"RED\"", gson.toJson(Color.RED));
     assertEquals("red", gson.fromJson("RED", Color.class).value);
   }
 
-  public enum Color {
+  enum Color {
     RED("red", 1), BLUE("blue", 2), GREEN("green", 3);
     String value;
     int index;
diff --git a/gson/src/test/java/com/google/gson/functional/EnumWithObfuscatedTest.java b/gson/src/test/java/com/google/gson/functional/EnumWithObfuscatedTest.java
index 080b81fa77..3acc08efef 100644
--- a/gson/src/test/java/com/google/gson/functional/EnumWithObfuscatedTest.java
+++ b/gson/src/test/java/com/google/gson/functional/EnumWithObfuscatedTest.java
@@ -16,26 +16,28 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.annotations.SerializedName;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for enums with Proguard.
  *
  * @author Young Cha
  */
-public class EnumWithObfuscatedTest extends TestCase {
+class EnumWithObfuscatedTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public enum Gender {
+  enum Gender {
     @SerializedName("MAIL")
     MALE,
 
@@ -43,7 +45,8 @@ public enum Gender {
     FEMALE
   }
 
-  public void testEnumClassWithObfuscated() {
+  @Test
+  void testEnumClassWithObfuscated() {
     for (Gender enumConstant: Gender.class.getEnumConstants()) {
       try {
         Gender.class.getField(enumConstant.name());
diff --git a/gson/src/test/java/com/google/gson/functional/EscapingTest.java b/gson/src/test/java/com/google/gson/functional/EscapingTest.java
index 1581f45189..1f4e66f029 100644
--- a/gson/src/test/java/com/google/gson/functional/EscapingTest.java
+++ b/gson/src/test/java/com/google/gson/functional/EscapingTest.java
@@ -16,12 +16,17 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import java.util.ArrayList;
 import java.util.List;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Performs some functional test involving JSON output escaping.
@@ -29,16 +34,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class EscapingTest extends TestCase {
+class EscapingTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testEscapingQuotesInStringArray() throws Exception {
+  @Test
+  void testEscapingQuotesInStringArray() throws Exception {
     String[] valueWithQuotes = { "beforeQuote\"afterQuote" };
     String jsonRepresentation = gson.toJson(valueWithQuotes);
     String[] target = gson.fromJson(jsonRepresentation, String[].class);
@@ -46,7 +51,8 @@ public void testEscapingQuotesInStringArray() throws Exception {
     assertEquals(valueWithQuotes[0], target[0]);
   }
 
-  public void testEscapeAllHtmlCharacters() {
+  @Test
+  void testEscapeAllHtmlCharacters() {
     List<String> strings = new ArrayList<String>();
     strings.add("<");
     strings.add(">");
@@ -58,7 +64,8 @@ public void testEscapeAllHtmlCharacters() {
         gson.toJson(strings));
   }
 
-  public void testEscapingObjectFields() throws Exception {
+  @Test
+  void testEscapingObjectFields() throws Exception {
     BagOfPrimitives objWithPrimitives = new BagOfPrimitives(1L, 1, true, "test with\" <script>");
     String jsonRepresentation = gson.toJson(objWithPrimitives);
     assertFalse(jsonRepresentation.contains("<"));
@@ -69,7 +76,8 @@ public void testEscapingObjectFields() throws Exception {
     assertEquals(objWithPrimitives.getExpectedJson(), expectedObject.getExpectedJson());
   }
   
-  public void testGsonAcceptsEscapedAndNonEscapedJsonDeserialization() throws Exception {
+  @Test
+  void testGsonAcceptsEscapedAndNonEscapedJsonDeserialization() throws Exception {
     Gson escapeHtmlGson = new GsonBuilder().create();
     Gson noEscapeHtmlGson = new GsonBuilder().disableHtmlEscaping().create();
     
@@ -82,7 +90,8 @@ public void testGsonAcceptsEscapedAndNonEscapedJsonDeserialization() throws Exce
     assertEquals(target, escapeHtmlGson.fromJson(nonEscapedJsonForm, BagOfPrimitives.class));
   }
 
-  public void testGsonDoubleDeserialization() {
+  @Test
+  void testGsonDoubleDeserialization() {
     BagOfPrimitives expected = new BagOfPrimitives(3L, 4, true, "value1");
     String json = gson.toJson(gson.toJson(expected));
     String value = gson.fromJson(json, String.class);
diff --git a/gson/src/test/java/com/google/gson/functional/ExclusionStrategyFunctionalTest.java b/gson/src/test/java/com/google/gson/functional/ExclusionStrategyFunctionalTest.java
index 2eca8bb4f9..5a1df5b14f 100644
--- a/gson/src/test/java/com/google/gson/functional/ExclusionStrategyFunctionalTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ExclusionStrategyFunctionalTest.java
@@ -16,6 +16,11 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.ExclusionStrategy;
 import com.google.gson.FieldAttributes;
 import com.google.gson.Gson;
@@ -26,7 +31,8 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Performs some functional tests when Gson is instantiated with some common user defined
@@ -35,7 +41,7 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ExclusionStrategyFunctionalTest extends TestCase {
+class ExclusionStrategyFunctionalTest {
   private static final ExclusionStrategy EXCLUDE_SAMPLE_OBJECT_FOR_TEST = new ExclusionStrategy() {
     @Override public boolean shouldSkipField(FieldAttributes f) {
       return false;
@@ -47,13 +53,13 @@ public class ExclusionStrategyFunctionalTest extends TestCase {
 
   private SampleObjectForTest src;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     src = new SampleObjectForTest();
   }
 
-  public void testExclusionStrategySerialization() throws Exception {
+  @Test
+  void testExclusionStrategySerialization() throws Exception {
     Gson gson = createGson(new MyExclusionStrategy(String.class), true);
     String json = gson.toJson(src);
     assertFalse(json.contains("\"stringField\""));
@@ -61,7 +67,8 @@ public void testExclusionStrategySerialization() throws Exception {
     assertTrue(json.contains("\"longField\""));
   }
 
-  public void testExclusionStrategySerializationDoesNotImpactDeserialization() {
+  @Test
+  void testExclusionStrategySerializationDoesNotImpactDeserialization() {
     String json = "{\"annotatedField\":1,\"stringField\":\"x\",\"longField\":2}";
     Gson gson = createGson(new MyExclusionStrategy(String.class), true);
     SampleObjectForTest value = gson.fromJson(json, SampleObjectForTest.class);
@@ -70,7 +77,8 @@ public void testExclusionStrategySerializationDoesNotImpactDeserialization() {
     assertEquals(2, value.longField);
   }
 
-  public void testExclusionStrategyDeserialization() throws Exception {
+  @Test
+  void testExclusionStrategyDeserialization() throws Exception {
     Gson gson = createGson(new MyExclusionStrategy(String.class), false);
     JsonObject json = new JsonObject();
     json.add("annotatedField", new JsonPrimitive(src.annotatedField + 5));
@@ -85,7 +93,8 @@ public void testExclusionStrategyDeserialization() throws Exception {
     assertEquals(src.stringField, target.stringField);
   }
 
-  public void testExclusionStrategySerializationDoesNotImpactSerialization() throws Exception {
+  @Test
+  void testExclusionStrategySerializationDoesNotImpactSerialization() throws Exception {
     Gson gson = createGson(new MyExclusionStrategy(String.class), false);
     String json = gson.toJson(src);
     assertTrue(json.contains("\"stringField\""));
@@ -93,7 +102,8 @@ public void testExclusionStrategySerializationDoesNotImpactSerialization() throw
     assertTrue(json.contains("\"longField\""));
   }
 
-  public void testExclusionStrategyWithMode() throws Exception {
+  @Test
+  void testExclusionStrategyWithMode() throws Exception {
     SampleObjectForTest testObj = new SampleObjectForTest(
         src.annotatedField + 5, src.stringField + "blah,blah",
         src.longField + 655L);
@@ -112,14 +122,16 @@ public void testExclusionStrategyWithMode() throws Exception {
     assertEquals(src.stringField, target.stringField);
   }
 
-  public void testExcludeTopLevelClassSerialization() {
+  @Test
+  void testExcludeTopLevelClassSerialization() {
     Gson gson = new GsonBuilder()
         .addSerializationExclusionStrategy(EXCLUDE_SAMPLE_OBJECT_FOR_TEST)
         .create();
     assertEquals("null", gson.toJson(new SampleObjectForTest(), SampleObjectForTest.class));
   }
 
-  public void testExcludeTopLevelClassSerializationDoesNotImpactDeserialization() {
+  @Test
+  void testExcludeTopLevelClassSerializationDoesNotImpactDeserialization() {
     Gson gson = new GsonBuilder()
         .addSerializationExclusionStrategy(EXCLUDE_SAMPLE_OBJECT_FOR_TEST)
         .create();
@@ -130,7 +142,8 @@ public void testExcludeTopLevelClassSerializationDoesNotImpactDeserialization()
     assertEquals(2, value.longField);
   }
 
-  public void testExcludeTopLevelClassDeserialization() {
+  @Test
+  void testExcludeTopLevelClassDeserialization() {
     Gson gson = new GsonBuilder()
         .addDeserializationExclusionStrategy(EXCLUDE_SAMPLE_OBJECT_FOR_TEST)
         .create();
@@ -139,7 +152,8 @@ public void testExcludeTopLevelClassDeserialization() {
     assertNull(value);
   }
 
-  public void testExcludeTopLevelClassDeserializationDoesNotImpactSerialization() {
+  @Test
+  void testExcludeTopLevelClassDeserializationDoesNotImpactSerialization() {
     Gson gson = new GsonBuilder()
         .addDeserializationExclusionStrategy(EXCLUDE_SAMPLE_OBJECT_FOR_TEST)
         .create();
diff --git a/gson/src/test/java/com/google/gson/functional/ExposeFieldsTest.java b/gson/src/test/java/com/google/gson/functional/ExposeFieldsTest.java
index 0430ba49d1..e264dbc8b5 100644
--- a/gson/src/test/java/com/google/gson/functional/ExposeFieldsTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ExposeFieldsTest.java
@@ -16,41 +16,46 @@
 
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.InstanceCreator;
 import com.google.gson.annotations.Expose;
-
-import junit.framework.TestCase;
+import java.lang.reflect.Type;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for the regarding functional "@Expose" type tests.
  *
  * @author Joel Leitch
  */
-public class ExposeFieldsTest extends TestCase {
+class ExposeFieldsTest {
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder()
         .excludeFieldsWithoutExposeAnnotation()
         .registerTypeAdapter(SomeInterface.class, new SomeInterfaceInstanceCreator())
         .create();
   }
 
-  public void testNullExposeFieldSerialization() throws Exception {
+  @Test
+  void testNullExposeFieldSerialization() throws Exception {
     ClassWithExposedFields object = new ClassWithExposedFields(null, 1);
     String json = gson.toJson(object);
 
     assertEquals(object.getExpectedJson(), json);
   }
 
-  public void testArrayWithOneNullExposeFieldObjectSerialization() throws Exception {
+  @Test
+  void testArrayWithOneNullExposeFieldObjectSerialization() throws Exception {
     ClassWithExposedFields object1 = new ClassWithExposedFields(1, 1);
     ClassWithExposedFields object2 = new ClassWithExposedFields(null, 1);
     ClassWithExposedFields object3 = new ClassWithExposedFields(2, 2);
@@ -66,12 +71,14 @@ public void testArrayWithOneNullExposeFieldObjectSerialization() throws Exceptio
     assertEquals(expected, json);
   }
 
-  public void testExposeAnnotationSerialization() throws Exception {
+  @Test
+  void testExposeAnnotationSerialization() throws Exception {
     ClassWithExposedFields target = new ClassWithExposedFields(1, 2);
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testExposeAnnotationDeserialization() throws Exception {
+  @Test
+  void testExposeAnnotationDeserialization() throws Exception {
     String json = "{a:3,b:4,d:20.0}";
     ClassWithExposedFields target = gson.fromJson(json, ClassWithExposedFields.class);
 
@@ -80,30 +87,34 @@ public void testExposeAnnotationDeserialization() throws Exception {
     assertFalse(target.d == 20);
   }
 
-  public void testNoExposedFieldSerialization() throws Exception {
+  @Test
+  void testNoExposedFieldSerialization() throws Exception {
     ClassWithNoExposedFields obj = new ClassWithNoExposedFields();
     String json = gson.toJson(obj);
 
     assertEquals("{}", json);
   }
 
-  public void testNoExposedFieldDeserialization() throws Exception {
+  @Test
+  void testNoExposedFieldDeserialization() throws Exception {
     String json = "{a:4,b:5}";
     ClassWithNoExposedFields obj = gson.fromJson(json, ClassWithNoExposedFields.class);
 
     assertEquals(0, obj.a);
     assertEquals(1, obj.b);
   }
-  
-  public void testExposedInterfaceFieldSerialization() throws Exception {
+
+  @Test
+  void testExposedInterfaceFieldSerialization() throws Exception {
     String expected = "{\"interfaceField\":{}}";
     ClassWithInterfaceField target = new ClassWithInterfaceField(new SomeObject());
     String actual = gson.toJson(target);
-    
+
     assertEquals(expected, actual);
   }
-  
-  public void testExposedInterfaceFieldDeserialization() throws Exception {
+
+  @Test
+  void testExposedInterfaceFieldDeserialization() throws Exception {
     String json = "{\"interfaceField\":{}}";
     ClassWithInterfaceField obj = gson.fromJson(json, ClassWithInterfaceField.class);
 
@@ -143,21 +154,21 @@ private static class ClassWithNoExposedFields {
     private final int a = 0;
     private final int b = 1;
   }
-  
+
   private static interface SomeInterface {
     // Empty interface
   }
-  
+
   private static class SomeObject implements SomeInterface {
     // Do nothing
   }
-  
+
   private static class SomeInterfaceInstanceCreator implements InstanceCreator<SomeInterface> {
     @Override public SomeInterface createInstance(Type type) {
       return new SomeObject();
     }
   }
-  
+
   private static class ClassWithInterfaceField {
     @Expose
     private final SomeInterface interfaceField;
@@ -165,5 +176,5 @@ private static class ClassWithInterfaceField {
     public ClassWithInterfaceField(SomeInterface interfaceField) {
       this.interfaceField = interfaceField;
     }
-  }  
+  }
 }
diff --git a/gson/src/test/java/com/google/gson/functional/FieldExclusionTest.java b/gson/src/test/java/com/google/gson/functional/FieldExclusionTest.java
index 080a8234fe..e5eadd06ea 100644
--- a/gson/src/test/java/com/google/gson/functional/FieldExclusionTest.java
+++ b/gson/src/test/java/com/google/gson/functional/FieldExclusionTest.java
@@ -16,10 +16,12 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Performs some functional testing to ensure GSON infrastructure properly serializes/deserializes
@@ -28,18 +30,18 @@
  *
  * @author Joel Leitch
  */
-public class FieldExclusionTest extends TestCase {
+class FieldExclusionTest {
   private static final String VALUE = "blah_1234";
 
   private Outer outer;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     outer = new Outer();
   }
 
-  public void testDefaultInnerClassExclusion() throws Exception {
+  @Test
+  void testDefaultInnerClassExclusion() throws Exception {
     Gson gson = new Gson();
     Outer.Inner target = outer.new Inner(VALUE);
     String result = gson.toJson(target);
@@ -51,14 +53,16 @@ public void testDefaultInnerClassExclusion() throws Exception {
     assertEquals(target.toJson(), result);
   }
 
-  public void testInnerClassExclusion() throws Exception {
+  @Test
+  void testInnerClassExclusion() throws Exception {
     Gson gson = new GsonBuilder().disableInnerClassSerialization().create();
     Outer.Inner target = outer.new Inner(VALUE);
     String result = gson.toJson(target);
     assertEquals("null", result);
   }
 
-  public void testDefaultNestedStaticClassIncluded() throws Exception {
+  @Test
+  void testDefaultNestedStaticClassIncluded() throws Exception {
     Gson gson = new Gson();
     Outer.Inner target = outer.new Inner(VALUE);
     String result = gson.toJson(target);
diff --git a/gson/src/test/java/com/google/gson/functional/FieldNamingTest.java b/gson/src/test/java/com/google/gson/functional/FieldNamingTest.java
index 04ba7b7cbe..28114ecec8 100644
--- a/gson/src/test/java/com/google/gson/functional/FieldNamingTest.java
+++ b/gson/src/test/java/com/google/gson/functional/FieldNamingTest.java
@@ -22,15 +22,17 @@
 import static com.google.gson.FieldNamingPolicy.UPPER_CAMEL_CASE;
 import static com.google.gson.FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES;
 import static com.google.gson.FieldNamingPolicy.UPPER_CASE_WITH_UNDERSCORES;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.FieldNamingPolicy;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.annotations.SerializedName;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class FieldNamingTest extends TestCase {
-  public void testIdentity() {
+class FieldNamingTest {
+  @Test
+  void testIdentity() {
     Gson gson = getGsonWithNamingPolicy(IDENTITY);
     assertEquals("{'lowerCamel':1,'UpperCamel':2,'_lowerCamelLeadingUnderscore':3," +
         "'_UpperCamelLeadingUnderscore':4,'lower_words':5,'UPPER_WORDS':6," +
@@ -38,7 +40,8 @@ public void testIdentity() {
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
-  public void testUpperCamelCase() {
+  @Test
+  void testUpperCamelCase() {
     Gson gson = getGsonWithNamingPolicy(UPPER_CAMEL_CASE);
     assertEquals("{'LowerCamel':1,'UpperCamel':2,'_LowerCamelLeadingUnderscore':3," +
         "'_UpperCamelLeadingUnderscore':4,'Lower_words':5,'UPPER_WORDS':6," +
@@ -46,7 +49,8 @@ public void testUpperCamelCase() {
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
-  public void testUpperCamelCaseWithSpaces() {
+  @Test
+  void testUpperCamelCaseWithSpaces() {
     Gson gson = getGsonWithNamingPolicy(UPPER_CAMEL_CASE_WITH_SPACES);
     assertEquals("{'Lower Camel':1,'Upper Camel':2,'_Lower Camel Leading Underscore':3," +
         "'_ Upper Camel Leading Underscore':4,'Lower_words':5,'U P P E R_ W O R D S':6," +
@@ -54,7 +58,8 @@ public void testUpperCamelCaseWithSpaces() {
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
-  public void testUpperCaseWithUnderscores() {
+  @Test
+  void testUpperCaseWithUnderscores() {
     Gson gson = getGsonWithNamingPolicy(UPPER_CASE_WITH_UNDERSCORES);
     assertEquals("{'LOWER_CAMEL':1,'UPPER_CAMEL':2,'_LOWER_CAMEL_LEADING_UNDERSCORE':3," +
         "'__UPPER_CAMEL_LEADING_UNDERSCORE':4,'LOWER_WORDS':5,'U_P_P_E_R__W_O_R_D_S':6," +
@@ -62,7 +67,8 @@ public void testUpperCaseWithUnderscores() {
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
-  public void testLowerCaseWithUnderscores() {
+  @Test
+  void testLowerCaseWithUnderscores() {
     Gson gson = getGsonWithNamingPolicy(LOWER_CASE_WITH_UNDERSCORES);
     assertEquals("{'lower_camel':1,'upper_camel':2,'_lower_camel_leading_underscore':3," +
         "'__upper_camel_leading_underscore':4,'lower_words':5,'u_p_p_e_r__w_o_r_d_s':6," +
@@ -70,7 +76,8 @@ public void testLowerCaseWithUnderscores() {
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
-  public void testLowerCaseWithDashes() {
+  @Test
+  void testLowerCaseWithDashes() {
     Gson gson = getGsonWithNamingPolicy(LOWER_CASE_WITH_DASHES);
     assertEquals("{'lower-camel':1,'upper-camel':2,'_lower-camel-leading-underscore':3," +
         "'_-upper-camel-leading-underscore':4,'lower_words':5,'u-p-p-e-r_-w-o-r-d-s':6," +
diff --git a/gson/src/test/java/com/google/gson/functional/GsonVersionDiagnosticsTest.java b/gson/src/test/java/com/google/gson/functional/GsonVersionDiagnosticsTest.java
index 36eff8e1e7..d73c7bcae5 100644
--- a/gson/src/test/java/com/google/gson/functional/GsonVersionDiagnosticsTest.java
+++ b/gson/src/test/java/com/google/gson/functional/GsonVersionDiagnosticsTest.java
@@ -15,32 +15,31 @@
  */
 package com.google.gson.functional;
 
-import java.io.IOException;
-import java.util.regex.Pattern;
-
-import org.junit.Before;
-import org.junit.Test;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.TypeAdapter;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
-
-import junit.framework.TestCase;
+import java.io.IOException;
+import java.util.regex.Pattern;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests to validate printing of Gson version on AssertionErrors
  *
  * @author Inderjeet Singh
  */
-public class GsonVersionDiagnosticsTest extends TestCase {
+class GsonVersionDiagnosticsTest {
   private static final Pattern GSON_VERSION_PATTERN = Pattern.compile("(\\(GSON \\d\\.\\d\\.\\d)(?:[-.][A-Z]+)?\\)$");
 
   private Gson gson;
 
-  @Before
-  public void setUp() {
+  @BeforeEach
+  void setUp() {
     gson = new GsonBuilder().registerTypeAdapter(TestType.class, new TypeAdapter<TestType>() {
       @Override public void write(JsonWriter out, TestType value) {
         throw new AssertionError("Expected during serialization");
@@ -52,13 +51,13 @@ public void setUp() {
   }
 
   @Test
-  public void testVersionPattern() {
+  void testVersionPattern() {
     assertTrue(GSON_VERSION_PATTERN.matcher("(GSON 2.8.5)").matches());
     assertTrue(GSON_VERSION_PATTERN.matcher("(GSON 2.8.5-SNAPSHOT)").matches());
   }
 
   @Test
-  public void testAssertionErrorInSerializationPrintsVersion() {
+  void testAssertionErrorInSerializationPrintsVersion() {
     try {
       gson.toJson(new TestType());
       fail();
@@ -68,7 +67,7 @@ public void testAssertionErrorInSerializationPrintsVersion() {
   }
 
   @Test
-  public void testAssertionErrorInDeserializationPrintsVersion() {
+  void testAssertionErrorInDeserializationPrintsVersion() {
     try {
       gson.fromJson("{'a':'abc'}", TestType.class);
       fail();
diff --git a/gson/src/test/java/com/google/gson/functional/InheritanceTest.java b/gson/src/test/java/com/google/gson/functional/InheritanceTest.java
index 475db83826..766c1aa728 100644
--- a/gson/src/test/java/com/google/gson/functional/InheritanceTest.java
+++ b/gson/src/test/java/com/google/gson/functional/InheritanceTest.java
@@ -15,6 +15,11 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
@@ -26,9 +31,6 @@
 import com.google.gson.common.TestTypes.ClassWithBaseField;
 import com.google.gson.common.TestTypes.Nested;
 import com.google.gson.common.TestTypes.Sub;
-
-import junit.framework.TestCase;
-
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.LinkedList;
@@ -37,30 +39,33 @@
 import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeSet;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
- * Functional tests for Json serialization and deserialization of classes with 
+ * Functional tests for Json serialization and deserialization of classes with
  * inheritance hierarchies.
  *
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class InheritanceTest extends TestCase {
+class InheritanceTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testSubClassSerialization() throws Exception {
+  @Test
+  void testSubClassSerialization() throws Exception {
     SubTypeOfNested target = new SubTypeOfNested(new BagOfPrimitives(10, 20, false, "stringValue"),
         new BagOfPrimitives(30, 40, true, "stringValue"));
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testSubClassDeserialization() throws Exception {
+  @Test
+  void testSubClassDeserialization() throws Exception {
     String json = "{\"value\":5,\"primitive1\":{\"longValue\":10,\"intValue\":20,"
         + "\"booleanValue\":false,\"stringValue\":\"stringValue\"},\"primitive2\":"
         + "{\"longValue\":30,\"intValue\":40,\"booleanValue\":true,"
@@ -69,68 +74,77 @@ public void testSubClassDeserialization() throws Exception {
     assertEquals(json, target.getExpectedJson());
   }
 
-  public void testClassWithBaseFieldSerialization() {
+  @Test
+  void testClassWithBaseFieldSerialization() {
     ClassWithBaseField sub = new ClassWithBaseField(new Sub());
     JsonObject json = (JsonObject) gson.toJsonTree(sub);
     JsonElement base = json.getAsJsonObject().get(ClassWithBaseField.FIELD_KEY);
     assertEquals(Sub.SUB_NAME, base.getAsJsonObject().get(Sub.SUB_FIELD_KEY).getAsString());
   }
 
-  public void testClassWithBaseArrayFieldSerialization() {
+  @Test
+  void testClassWithBaseArrayFieldSerialization() {
     Base[] baseClasses = new Base[]{ new Sub(), new Sub()};
     ClassWithBaseArrayField sub = new ClassWithBaseArrayField(baseClasses);
     JsonObject json = gson.toJsonTree(sub).getAsJsonObject();
     JsonArray bases = json.get(ClassWithBaseArrayField.FIELD_KEY).getAsJsonArray();
-    for (JsonElement element : bases) { 
+    for (JsonElement element : bases) {
       assertEquals(Sub.SUB_NAME, element.getAsJsonObject().get(Sub.SUB_FIELD_KEY).getAsString());
     }
   }
 
-  public void testClassWithBaseCollectionFieldSerialization() {
+  @Test
+  void testClassWithBaseCollectionFieldSerialization() {
     Collection<Base> baseClasses = new ArrayList<Base>();
     baseClasses.add(new Sub());
     baseClasses.add(new Sub());
     ClassWithBaseCollectionField sub = new ClassWithBaseCollectionField(baseClasses);
     JsonObject json = gson.toJsonTree(sub).getAsJsonObject();
     JsonArray bases = json.get(ClassWithBaseArrayField.FIELD_KEY).getAsJsonArray();
-    for (JsonElement element : bases) { 
+    for (JsonElement element : bases) {
       assertEquals(Sub.SUB_NAME, element.getAsJsonObject().get(Sub.SUB_FIELD_KEY).getAsString());
     }
   }
 
-  public void testBaseSerializedAsSub() {
+  @Test
+  void testBaseSerializedAsSub() {
     Base base = new Sub();
     JsonObject json = gson.toJsonTree(base).getAsJsonObject();
     assertEquals(Sub.SUB_NAME, json.get(Sub.SUB_FIELD_KEY).getAsString());
   }
 
-  public void testBaseSerializedAsSubForToJsonMethod() {
+  @Test
+  void testBaseSerializedAsSubForToJsonMethod() {
     Base base = new Sub();
     String json = gson.toJson(base);
     assertTrue(json.contains(Sub.SUB_NAME));
   }
 
-  public void testBaseSerializedAsBaseWhenSpecifiedWithExplicitType() {
+  @Test
+  void testBaseSerializedAsBaseWhenSpecifiedWithExplicitType() {
     Base base = new Sub();
     JsonObject json = gson.toJsonTree(base, Base.class).getAsJsonObject();
     assertEquals(Base.BASE_NAME, json.get(Base.BASE_FIELD_KEY).getAsString());
     assertNull(json.get(Sub.SUB_FIELD_KEY));
   }
 
-  public void testBaseSerializedAsBaseWhenSpecifiedWithExplicitTypeForToJsonMethod() {
+  @Test
+  void testBaseSerializedAsBaseWhenSpecifiedWithExplicitTypeForToJsonMethod() {
     Base base = new Sub();
     String json = gson.toJson(base, Base.class);
     assertTrue(json.contains(Base.BASE_NAME));
     assertFalse(json.contains(Sub.SUB_FIELD_KEY));
   }
 
-  public void testBaseSerializedAsSubWhenSpecifiedWithExplicitType() {
+  @Test
+  void testBaseSerializedAsSubWhenSpecifiedWithExplicitType() {
     Base base = new Sub();
     JsonObject json = gson.toJsonTree(base, Sub.class).getAsJsonObject();
     assertEquals(Sub.SUB_NAME, json.get(Sub.SUB_FIELD_KEY).getAsString());
   }
 
-  public void testBaseSerializedAsSubWhenSpecifiedWithExplicitTypeForToJsonMethod() {
+  @Test
+  void testBaseSerializedAsSubWhenSpecifiedWithExplicitTypeForToJsonMethod() {
     Base base = new Sub();
     String json = gson.toJson(base, Sub.class);
     assertTrue(json.contains(Sub.SUB_NAME));
@@ -150,7 +164,8 @@ public void appendFields(StringBuilder sb) {
     }
   }
 
-  public void testSubInterfacesOfCollectionSerialization() throws Exception {
+  @Test
+  void testSubInterfacesOfCollectionSerialization() throws Exception {
     List<Integer> list = new LinkedList<Integer>();
     list.add(0);
     list.add(1);
@@ -176,18 +191,19 @@ public void testSubInterfacesOfCollectionSerialization() throws Exception {
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testSubInterfacesOfCollectionDeserialization() throws Exception {
+  @Test
+  void testSubInterfacesOfCollectionDeserialization() throws Exception {
     String json = "{\"list\":[0,1,2,3],\"queue\":[0,1,2,3],\"set\":[0.1,0.2,0.3,0.4],"
         + "\"sortedSet\":[\"a\",\"b\",\"c\",\"d\"]"
         + "}";
-    ClassWithSubInterfacesOfCollection target = 
+    ClassWithSubInterfacesOfCollection target =
       gson.fromJson(json, ClassWithSubInterfacesOfCollection.class);
     assertTrue(target.listContains(0, 1, 2, 3));
     assertTrue(target.queueContains(0, 1, 2, 3));
     assertTrue(target.setContains(0.1F, 0.2F, 0.3F, 0.4F));
     assertTrue(target.sortedSetContains('a', 'b', 'c', 'd'));
   }
-  
+
   private static class ClassWithSubInterfacesOfCollection {
     private List<Integer> list;
     private Queue<Long> queue;
@@ -210,7 +226,7 @@ boolean listContains(int... values) {
       }
       return true;
     }
-    
+
     boolean queueContains(long... values) {
       for (long value : values) {
         if (!queue.contains(value)) {
@@ -219,7 +235,7 @@ boolean queueContains(long... values) {
       }
       return true;
     }
-    
+
     boolean setContains(float... values) {
       for (float value : values) {
         if (!set.contains(value)) {
@@ -237,7 +253,7 @@ boolean sortedSetContains(char... values) {
       }
       return true;
     }
-    
+
     public String getExpectedJson() {
       StringBuilder sb = new StringBuilder();
       sb.append("{");
diff --git a/gson/src/test/java/com/google/gson/functional/InstanceCreatorTest.java b/gson/src/test/java/com/google/gson/functional/InstanceCreatorTest.java
index 5437c876e1..5b80e74141 100644
--- a/gson/src/test/java/com/google/gson/functional/InstanceCreatorTest.java
+++ b/gson/src/test/java/com/google/gson/functional/InstanceCreatorTest.java
@@ -16,21 +16,23 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.InstanceCreator;
 import com.google.gson.common.TestTypes.Base;
 import com.google.gson.common.TestTypes.ClassWithBaseField;
 import com.google.gson.common.TestTypes.Sub;
-
 import com.google.gson.reflect.TypeToken;
+import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.List;
-import junit.framework.TestCase;
-
-import java.lang.reflect.Type;
 import java.util.SortedSet;
 import java.util.TreeSet;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional Test exercising custom serialization only. When test applies to both
@@ -38,9 +40,10 @@
  *
  * @author Inderjeet Singh
  */
-public class InstanceCreatorTest extends TestCase {
+class InstanceCreatorTest {
 
-  public void testInstanceCreatorReturnsBaseType() {
+  @Test
+  void testInstanceCreatorReturnsBaseType() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Base.class, new InstanceCreator<Base>() {
         @Override public Base createInstance(Type type) {
@@ -53,7 +56,8 @@ public void testInstanceCreatorReturnsBaseType() {
     assertEquals("BaseRevised", base.baseName);
   }
 
-  public void testInstanceCreatorReturnsSubTypeForTopLevelObject() {
+  @Test
+  void testInstanceCreatorReturnsSubTypeForTopLevelObject() {
     Gson gson = new GsonBuilder()
     .registerTypeAdapter(Base.class, new InstanceCreator<Base>() {
       @Override public Base createInstance(Type type) {
@@ -71,7 +75,8 @@ public void testInstanceCreatorReturnsSubTypeForTopLevelObject() {
     assertEquals(Sub.SUB_NAME, sub.subName);
   }
 
-  public void testInstanceCreatorReturnsSubTypeForField() {
+  @Test
+  void testInstanceCreatorReturnsSubTypeForField() {
     Gson gson = new GsonBuilder()
     .registerTypeAdapter(Base.class, new InstanceCreator<Base>() {
       @Override public Base createInstance(Type type) {
@@ -86,7 +91,8 @@ public void testInstanceCreatorReturnsSubTypeForField() {
   }
 
   // This regressed in Gson 2.0 and 2.1
-  public void testInstanceCreatorForCollectionType() {
+  @Test
+  void testInstanceCreatorForCollectionType() {
     @SuppressWarnings("serial")
     class SubArrayList<T> extends ArrayList<T> {}
     InstanceCreator<List<String>> listCreator = new InstanceCreator<List<String>>() {
@@ -102,13 +108,13 @@ class SubArrayList<T> extends ArrayList<T> {}
     assertEquals(SubArrayList.class, list.getClass());
   }
 
-  @SuppressWarnings({ "unchecked", "rawtypes" })
-  public void testInstanceCreatorForParametrizedType() throws Exception {
+  @Test
+  void testInstanceCreatorForParametrizedType() throws Exception {
     @SuppressWarnings("serial")
     class SubTreeSet<T> extends TreeSet<T> {}
-    InstanceCreator<SortedSet> sortedSetCreator = new InstanceCreator<SortedSet>() {
-      @Override public SortedSet createInstance(Type type) {
-        return new SubTreeSet();
+    InstanceCreator<SortedSet<?>> sortedSetCreator = new InstanceCreator<SortedSet<?>>() {
+      @Override public SortedSet<?> createInstance(Type type) {
+        return new SubTreeSet<Object>();
       }
     };
     Gson gson = new GsonBuilder()
@@ -116,7 +122,7 @@ class SubTreeSet<T> extends TreeSet<T> {}
         .create();
 
     Type sortedSetType = new TypeToken<SortedSet<String>>() {}.getType();
-    SortedSet<String> set = gson.fromJson("[\"a\"]", sortedSetType);
+    SortedSet<?> set = gson.fromJson("[\"a\"]", sortedSetType);
     assertEquals(set.first(), "a");
     assertEquals(SubTreeSet.class, set.getClass());
 
diff --git a/gson/src/test/java/com/google/gson/functional/InterfaceTest.java b/gson/src/test/java/com/google/gson/functional/InterfaceTest.java
index 6851f1e99b..6f43bc7bd5 100644
--- a/gson/src/test/java/com/google/gson/functional/InterfaceTest.java
+++ b/gson/src/test/java/com/google/gson/functional/InterfaceTest.java
@@ -16,9 +16,11 @@
 
 package com.google.gson.functional;
 
-import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import junit.framework.TestCase;
+import com.google.gson.Gson;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests involving interfaces.
@@ -26,24 +28,25 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class InterfaceTest extends TestCase {
+class InterfaceTest {
   private static final String OBJ_JSON = "{\"someStringValue\":\"StringValue\"}";
 
   private Gson gson;
   private TestObject obj;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
     obj = new TestObject("StringValue");
   }
 
-  public void testSerializingObjectImplementingInterface() throws Exception {
+  @Test
+  void testSerializingObjectImplementingInterface() throws Exception {
     assertEquals(OBJ_JSON, gson.toJson(obj));
   }
-  
-  public void testSerializingInterfaceObjectField() throws Exception {
+
+  @Test
+  void testSerializingInterfaceObjectField() throws Exception {
     TestObjectWrapper objWrapper = new TestObjectWrapper(obj);
     assertEquals("{\"obj\":" + OBJ_JSON + "}", gson.toJson(objWrapper));
   }
@@ -51,11 +54,11 @@ public void testSerializingInterfaceObjectField() throws Exception {
   private static interface TestObjectInterface {
     // Holder
   }
-  
+
   private static class TestObject implements TestObjectInterface {
     @SuppressWarnings("unused")
     private String someStringValue;
-    
+
     private TestObject(String value) {
       this.someStringValue = value;
     }
@@ -64,7 +67,7 @@ private TestObject(String value) {
   private static class TestObjectWrapper {
     @SuppressWarnings("unused")
     private TestObjectInterface obj;
-    
+
     private TestObjectWrapper(TestObjectInterface obj) {
       this.obj = obj;
     }
diff --git a/gson/src/test/java/com/google/gson/functional/InternationalizationTest.java b/gson/src/test/java/com/google/gson/functional/InternationalizationTest.java
index 169c37a503..ba4abf1abd 100644
--- a/gson/src/test/java/com/google/gson/functional/InternationalizationTest.java
+++ b/gson/src/test/java/com/google/gson/functional/InternationalizationTest.java
@@ -16,26 +16,28 @@
 
 package com.google.gson.functional;
 
-import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import junit.framework.TestCase;
+import com.google.gson.Gson;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for internationalized strings.
  *
  * @author Inderjeet Singh
  */
-public class InternationalizationTest extends TestCase {
+class InternationalizationTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
   /*
-  public void testStringsWithRawChineseCharactersSerialization() throws Exception {
+  @Test
+  void testStringsWithRawChineseCharactersSerialization() throws Exception {
     String target = "好好好";
     String json = gson.toJson(target);
     String expected = "\"\\u597d\\u597d\\u597d\"";
@@ -43,28 +45,32 @@ public void testStringsWithRawChineseCharactersSerialization() throws Exception
   }
   */
 
-  public void testStringsWithRawChineseCharactersDeserialization() throws Exception {
+  @Test
+  void testStringsWithRawChineseCharactersDeserialization() throws Exception {
     String expected = "好好好";
     String json = "\"" + expected + "\"";
     String actual = gson.fromJson(json, String.class);
     assertEquals(expected, actual);
   }
 
-  public void testStringsWithUnicodeChineseCharactersSerialization() throws Exception {
+  @Test
+  void testStringsWithUnicodeChineseCharactersSerialization() throws Exception {
     String target = "\u597d\u597d\u597d";
     String json = gson.toJson(target);
     String expected = "\"\u597d\u597d\u597d\"";
     assertEquals(expected, json);
   }
 
-  public void testStringsWithUnicodeChineseCharactersDeserialization() throws Exception {
+  @Test
+  void testStringsWithUnicodeChineseCharactersDeserialization() throws Exception {
     String expected = "\u597d\u597d\u597d";
     String json = "\"" + expected + "\"";
     String actual = gson.fromJson(json, String.class);
     assertEquals(expected, actual);
   }
 
-  public void testStringsWithUnicodeChineseCharactersEscapedDeserialization() throws Exception {
+  @Test
+  void testStringsWithUnicodeChineseCharactersEscapedDeserialization() throws Exception {
     String actual = gson.fromJson("'\\u597d\\u597d\\u597d'", String.class);
     assertEquals("\u597d\u597d\u597d", actual);
   }
diff --git a/gson/src/test/java/com/google/gson/functional/JavaUtilConcurrentAtomicTest.java b/gson/src/test/java/com/google/gson/functional/JavaUtilConcurrentAtomicTest.java
index 464892a3a6..ea35b618e1 100644
--- a/gson/src/test/java/com/google/gson/functional/JavaUtilConcurrentAtomicTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JavaUtilConcurrentAtomicTest.java
@@ -16,52 +16,57 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.LongSerializationPolicy;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicIntegerArray;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicLongArray;
-
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.LongSerializationPolicy;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional test for Json serialization and deserialization for classes in java.util.concurrent.atomic
  */
-public class JavaUtilConcurrentAtomicTest extends TestCase {
+class JavaUtilConcurrentAtomicTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testAtomicBoolean() throws Exception {
+  @Test
+  void testAtomicBoolean() throws Exception {
     AtomicBoolean target = gson.fromJson("true", AtomicBoolean.class);
     assertTrue(target.get());
     String json = gson.toJson(target);
     assertEquals("true", json);
   }
 
-  public void testAtomicInteger() throws Exception {
+  @Test
+  void testAtomicInteger() throws Exception {
     AtomicInteger target = gson.fromJson("10", AtomicInteger.class);
     assertEquals(10, target.get());
     String json = gson.toJson(target);
     assertEquals("10", json);
   }
 
-  public void testAtomicLong() throws Exception {
+  @Test
+  void testAtomicLong() throws Exception {
     AtomicLong target = gson.fromJson("10", AtomicLong.class);
     assertEquals(10, target.get());
     String json = gson.toJson(target);
     assertEquals("10", json);
   }
 
-  public void testAtomicLongWithStringSerializationPolicy() throws Exception {
+  @Test
+  void testAtomicLongWithStringSerializationPolicy() throws Exception {
     Gson gson = new GsonBuilder()
         .setLongSerializationPolicy(LongSerializationPolicy.STRING)
         .create();
@@ -71,7 +76,8 @@ public void testAtomicLongWithStringSerializationPolicy() throws Exception {
     assertEquals("{\"value\":\"10\"}", json);
   }
 
-  public void testAtomicIntegerArray() throws Exception {
+  @Test
+  void testAtomicIntegerArray() throws Exception {
     AtomicIntegerArray target = gson.fromJson("[10, 13, 14]", AtomicIntegerArray.class);
     assertEquals(3, target.length());
     assertEquals(10, target.get(0));
@@ -81,7 +87,8 @@ public void testAtomicIntegerArray() throws Exception {
     assertEquals("[10,13,14]", json);
   }
 
-  public void testAtomicLongArray() throws Exception {
+  @Test
+  void testAtomicLongArray() throws Exception {
     AtomicLongArray target = gson.fromJson("[10, 13, 14]", AtomicLongArray.class);
     assertEquals(3, target.length());
     assertEquals(10, target.get(0));
@@ -91,7 +98,8 @@ public void testAtomicLongArray() throws Exception {
     assertEquals("[10,13,14]", json);
   }
 
-  public void testAtomicLongArrayWithStringSerializationPolicy() throws Exception {
+  @Test
+  void testAtomicLongArrayWithStringSerializationPolicy() throws Exception {
     Gson gson = new GsonBuilder()
         .setLongSerializationPolicy(LongSerializationPolicy.STRING)
         .create();
diff --git a/gson/src/test/java/com/google/gson/functional/JavaUtilTest.java b/gson/src/test/java/com/google/gson/functional/JavaUtilTest.java
index 0520965339..d27bae2ddc 100644
--- a/gson/src/test/java/com/google/gson/functional/JavaUtilTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JavaUtilTest.java
@@ -16,26 +16,29 @@
 
 package com.google.gson.functional;
 
-import java.util.Currency;
-import java.util.Properties;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
-
-import junit.framework.TestCase;
+import java.util.Currency;
+import java.util.Properties;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional test for Json serialization and deserialization for classes in java.util
  */
-public class JavaUtilTest extends TestCase {
+class JavaUtilTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testCurrency() throws Exception {
+  @Test
+  void testCurrency() throws Exception {
     CurrencyHolder target = gson.fromJson("{'value':'USD'}", CurrencyHolder.class);
     assertEquals("USD", target.value.getCurrencyCode());
     String json = gson.toJson(target);
@@ -51,7 +54,8 @@ private static class CurrencyHolder {
     Currency value;
   }
 
-  public void testProperties() {
+  @Test
+  void testProperties() {
     Properties props = gson.fromJson("{'a':'v1','b':'v2'}", Properties.class);
     assertEquals("v1", props.getProperty("a"));
     assertEquals("v2", props.getProperty("b"));
diff --git a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
index 4288bfe3bf..f3207c5a1e 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
@@ -16,6 +16,11 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -34,14 +39,15 @@
 import java.io.IOException;
 import java.lang.reflect.Type;
 import java.util.Locale;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the {@link com.google.gson.annotations.JsonAdapter} annotation on classes.
  */
-public final class JsonAdapterAnnotationOnClassesTest extends TestCase {
+class JsonAdapterAnnotationOnClassesTest {
 
-  public void testJsonAdapterInvoked() {
+  @Test
+  void testJsonAdapterInvoked() {
     Gson gson = new Gson();
     String json = gson.toJson(new A("bar"));
     assertEquals("\"jsonAdapter\"", json);
@@ -59,7 +65,8 @@ public void testJsonAdapterInvoked() {
     assertEquals(Foo.BAZ, baz);
   }
 
-  public void testJsonAdapterFactoryInvoked() {
+  @Test
+  void testJsonAdapterFactoryInvoked() {
     Gson gson = new Gson();
     String json = gson.toJson(new C("bar"));
     assertEquals("\"jsonAdapterFactory\"", json);
@@ -67,7 +74,8 @@ public void testJsonAdapterFactoryInvoked() {
     assertEquals("jsonAdapterFactory", c.value);
   }
 
-  public void testRegisteredAdapterOverridesJsonAdapter() {
+  @Test
+  void testRegisteredAdapterOverridesJsonAdapter() {
     TypeAdapter<A> typeAdapter = new TypeAdapter<A>() {
       @Override public void write(JsonWriter out, A value) throws IOException {
         out.value("registeredAdapter");
@@ -86,9 +94,10 @@ public void testRegisteredAdapterOverridesJsonAdapter() {
   /**
    * The serializer overrides field adapter, but for deserializer the fieldAdapter is used.
    */
-  public void testRegisteredSerializerOverridesJsonAdapter() {
+  @Test
+  void testRegisteredSerializerOverridesJsonAdapter() {
     JsonSerializer<A> serializer = new JsonSerializer<A>() {
-      public JsonElement serialize(A src, Type typeOfSrc,
+      @Override public JsonElement serialize(A src, Type typeOfSrc,
           JsonSerializationContext context) {
         return new JsonPrimitive("registeredSerializer");
       }
@@ -105,9 +114,10 @@ public JsonElement serialize(A src, Type typeOfSrc,
   /**
    * The deserializer overrides Json adapter, but for serializer the jsonAdapter is used.
    */
-  public void testRegisteredDeserializerOverridesJsonAdapter() {
+  @Test
+  void testRegisteredDeserializerOverridesJsonAdapter() {
     JsonDeserializer<A> deserializer = new JsonDeserializer<A>() {
-      public A deserialize(JsonElement json, Type typeOfT,
+      @Override public A deserialize(JsonElement json, Type typeOfT,
           JsonDeserializationContext context) throws JsonParseException {
         return new A("registeredDeserializer");
       }
@@ -121,19 +131,22 @@ public A deserialize(JsonElement json, Type typeOfT,
     assertEquals("registeredDeserializer", target.value);
   }
 
-  public void testIncorrectTypeAdapterFails() {
+  @Test
+  void testIncorrectTypeAdapterFails() {
     try {
       String json = new Gson().toJson(new ClassWithIncorrectJsonAdapter("bar"));
       fail(json);
     } catch (ClassCastException expected) {}
   }
 
-  public void testSuperclassTypeAdapterNotInvoked() {
+  @Test
+  void testSuperclassTypeAdapterNotInvoked() {
     String json = new Gson().toJson(new B("bar"));
     assertFalse(json.contains("jsonAdapter"));
   }
 
-  public void testNullSafeObjectFromJson() {
+  @Test
+  void testNullSafeObjectFromJson() {
     Gson gson = new Gson();
     NullableClass fromJson = gson.fromJson("null", NullableClass.class);
     assertNull(fromJson);
@@ -250,7 +263,8 @@ private static class FooJsonAdapter extends TypeAdapter<Foo> {
     }
   }
 
-  public void testIncorrectJsonAdapterType() {
+  @Test
+  void testIncorrectJsonAdapterType() {
     try {
       new Gson().toJson(new D());
       fail();
diff --git a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
index 706fe60f85..5d29e06c14 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
@@ -16,9 +16,9 @@
 
 package com.google.gson.functional;
 
-import java.io.IOException;
-import java.util.Arrays;
-import java.util.List;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -28,14 +28,17 @@
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
-
-import junit.framework.TestCase;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the {@link com.google.gson.annotations.JsonAdapter} annotation on fields.
  */
-public final class JsonAdapterAnnotationOnFieldsTest extends TestCase {
-  public void testClassAnnotationAdapterTakesPrecedenceOverDefault() {
+class JsonAdapterAnnotationOnFieldsTest {
+  @Test
+  void testClassAnnotationAdapterTakesPrecedenceOverDefault() {
     Gson gson = new Gson();
     String json = gson.toJson(new Computer(new User("Inderjeet Singh")));
     assertEquals("{\"user\":\"UserClassAnnotationAdapter\"}", json);
@@ -43,7 +46,8 @@ public void testClassAnnotationAdapterTakesPrecedenceOverDefault() {
     assertEquals("UserClassAnnotationAdapter", computer.user.name);
   }
 
-  public void testClassAnnotationAdapterFactoryTakesPrecedenceOverDefault() {
+  @Test
+  void testClassAnnotationAdapterFactoryTakesPrecedenceOverDefault() {
     Gson gson = new Gson();
     String json = gson.toJson(new Gizmo(new Part("Part")));
     assertEquals("{\"part\":\"GizmoPartTypeAdapterFactory\"}", json);
@@ -51,7 +55,8 @@ public void testClassAnnotationAdapterFactoryTakesPrecedenceOverDefault() {
     assertEquals("GizmoPartTypeAdapterFactory", computer.part.name);
   }
 
-  public void testRegisteredTypeAdapterTakesPrecedenceOverClassAnnotationAdapter() {
+  @Test
+  void testRegisteredTypeAdapterTakesPrecedenceOverClassAnnotationAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(User.class, new RegisteredUserAdapter())
         .create();
@@ -61,7 +66,8 @@ public void testRegisteredTypeAdapterTakesPrecedenceOverClassAnnotationAdapter()
     assertEquals("RegisteredUserAdapter", computer.user.name);
   }
 
-  public void testFieldAnnotationTakesPrecedenceOverRegisteredTypeAdapter() {
+  @Test
+  void testFieldAnnotationTakesPrecedenceOverRegisteredTypeAdapter() {
     Gson gson = new GsonBuilder()
       .registerTypeAdapter(Part.class, new TypeAdapter<Part>() {
         @Override public void write(JsonWriter out, Part part) throws IOException {
@@ -77,7 +83,8 @@ public void testFieldAnnotationTakesPrecedenceOverRegisteredTypeAdapter() {
     assertEquals("PartJsonFieldAnnotationAdapter", gadget.part.name);
   }
 
-  public void testFieldAnnotationTakesPrecedenceOverClassAnnotation() {
+  @Test
+  void testFieldAnnotationTakesPrecedenceOverClassAnnotation() {
     Gson gson = new Gson();
     String json = gson.toJson(new Computer2(new User("Inderjeet Singh")));
     assertEquals("{\"user\":\"UserFieldAnnotationAdapter\"}", json);
@@ -187,7 +194,8 @@ private static final class RegisteredUserAdapter extends TypeAdapter<User> {
     }
   }
 
-  public void testJsonAdapterInvokedOnlyForAnnotatedFields() {
+  @Test
+  void testJsonAdapterInvokedOnlyForAnnotatedFields() {
     Gson gson = new Gson();
     String json = "{'part1':'name','part2':{'name':'name2'}}";
     GadgetWithTwoParts gadget = gson.fromJson(json, GadgetWithTwoParts.class);
@@ -204,7 +212,8 @@ private static final class GadgetWithTwoParts {
     }
   }
 
-  public void testJsonAdapterWrappedInNullSafeAsRequested() {
+  @Test
+  void testJsonAdapterWrappedInNullSafeAsRequested() {
     Gson gson = new Gson();
     String fromJson = "{'part':null}";
 
@@ -225,7 +234,8 @@ private GadgetWithOptionalPart(Part part) {
   }
 
   /** Regression test contributed through https://github.com/google/gson/issues/831 */
-  public void testNonPrimitiveFieldAnnotationTakesPrecedenceOverDefault() {
+  @Test
+  void testNonPrimitiveFieldAnnotationTakesPrecedenceOverDefault() {
     Gson gson = new Gson();
     String json = gson.toJson(new GadgetWithOptionalPart(new Part("foo")));
     assertEquals("{\"part\":\"PartJsonFieldAnnotationAdapter\"}", json);
@@ -234,7 +244,8 @@ public void testNonPrimitiveFieldAnnotationTakesPrecedenceOverDefault() {
   }
 
   /** Regression test contributed through https://github.com/google/gson/issues/831 */
-  public void testPrimitiveFieldAnnotationTakesPrecedenceOverDefault() {
+  @Test
+  void testPrimitiveFieldAnnotationTakesPrecedenceOverDefault() {
     Gson gson = new Gson();
     String json = gson.toJson(new GadgetWithPrimitivePart(42));
     assertEquals("{\"part\":\"42\"}", json);
@@ -273,7 +284,8 @@ private static final class LongToStringTypeAdapterFactory implements TypeAdapter
     }
   }
 
-  public void testFieldAnnotationWorksForParameterizedType() {
+  @Test
+  void testFieldAnnotationWorksForParameterizedType() {
     Gson gson = new Gson();
     String json = gson.toJson(new Gizmo2(Arrays.asList(new Part("Part"))));
     assertEquals("{\"part\":\"GizmoPartTypeAdapterFactory\"}", json);
diff --git a/gson/src/test/java/com/google/gson/functional/JsonAdapterSerializerDeserializerTest.java b/gson/src/test/java/com/google/gson/functional/JsonAdapterSerializerDeserializerTest.java
index 8ab4e128a6..ef1d19c617 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonAdapterSerializerDeserializerTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonAdapterSerializerDeserializerTest.java
@@ -16,7 +16,8 @@
 
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
 import com.google.gson.JsonDeserializationContext;
@@ -27,16 +28,17 @@
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import com.google.gson.annotations.JsonAdapter;
-
-import junit.framework.TestCase;
+import java.lang.reflect.Type;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the {@link JsonAdapter} annotation on fields where the value is of
  * type {@link JsonSerializer} or {@link JsonDeserializer}.
  */
-public final class JsonAdapterSerializerDeserializerTest extends TestCase {
+class JsonAdapterSerializerDeserializerTest {
 
-  public void testJsonSerializerDeserializerBasedJsonAdapterOnFields() {
+  @Test
+  void testJsonSerializerDeserializerBasedJsonAdapterOnFields() {
     Gson gson = new Gson();
     String json = gson.toJson(new Computer(new User("Inderjeet Singh"), null, new User("Jesse Wilson")));
     assertEquals("{\"user1\":\"UserSerializer\",\"user3\":\"UserSerializerDeserializer\"}", json);
@@ -90,7 +92,8 @@ public User deserialize(JsonElement json, Type typeOfT, JsonDeserializationConte
     }
   }
 
-  public void testJsonSerializerDeserializerBasedJsonAdapterOnClass() {
+  @Test
+  void testJsonSerializerDeserializerBasedJsonAdapterOnClass() {
     Gson gson = new Gson();
     String json = gson.toJson(new Computer2(new User2("Inderjeet Singh")));
     assertEquals("{\"user\":\"UserSerializerDeserializer2\"}", json);
@@ -125,7 +128,8 @@ public User2 deserialize(JsonElement json, Type typeOfT, JsonDeserializationCont
     }
   }
 
-  public void testDifferentJsonAdaptersForGenericFieldsOfSameRawType() {
+  @Test
+  void testDifferentJsonAdaptersForGenericFieldsOfSameRawType() {
     Container c = new Container("Foo", 10);
     Gson gson = new Gson();
     String json = gson.toJson(c);
diff --git a/gson/src/test/java/com/google/gson/functional/JsonArrayTest.java b/gson/src/test/java/com/google/gson/functional/JsonArrayTest.java
index 22a479b85d..af08185e4c 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonArrayTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonArrayTest.java
@@ -16,19 +16,21 @@
 
 package com.google.gson.functional;
 
-import com.google.gson.JsonArray;
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import com.google.gson.JsonArray;
 import java.math.BigInteger;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for adding primitives to a JsonArray.
  *
  * @author Dillon Dixon
  */
-public class JsonArrayTest extends TestCase {
+class JsonArrayTest {
 
-  public void testStringPrimitiveAddition() {
+  @Test
+  void testStringPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add("Hello");
@@ -40,7 +42,8 @@ public void testStringPrimitiveAddition() {
     assertEquals("[\"Hello\",\"Goodbye\",\"Thank you\",null,\"Yes\"]", jsonArray.toString());
   }
 
-  public void testIntegerPrimitiveAddition() {
+  @Test
+  void testIntegerPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     int x = 1;
@@ -63,7 +66,8 @@ public void testIntegerPrimitiveAddition() {
     assertEquals("[1,2,-3,null,4,0]", jsonArray.toString());
   }
 
-  public void testDoublePrimitiveAddition() {
+  @Test
+  void testDoublePrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     double x = 1.0;
@@ -85,7 +89,8 @@ public void testDoublePrimitiveAddition() {
     assertEquals("[1.0,2.13232,0.121,null,-0.00234,null]", jsonArray.toString());
   }
 
-  public void testBooleanPrimitiveAddition() {
+  @Test
+  void testBooleanPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add(true);
@@ -98,7 +103,8 @@ public void testBooleanPrimitiveAddition() {
     assertEquals("[true,true,false,false,null,true]", jsonArray.toString());
   }
 
-  public void testCharPrimitiveAddition() {
+  @Test
+  void testCharPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add('a');
@@ -112,7 +118,8 @@ public void testCharPrimitiveAddition() {
     assertEquals("[\"a\",\"e\",\"i\",\"o\",null,\"u\",\"and sometimes Y\"]", jsonArray.toString());
   }
 
-  public void testMixedPrimitiveAddition() {
+  @Test
+  void testMixedPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add('a');
@@ -127,7 +134,8 @@ public void testMixedPrimitiveAddition() {
     assertEquals("[\"a\",\"apple\",12121,\"o\",null,null,12.232,2323]", jsonArray.toString());
   }
 
-  public void testNullPrimitiveAddition() {
+  @Test
+  void testNullPrimitiveAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add((Character) null);
@@ -143,7 +151,8 @@ public void testNullPrimitiveAddition() {
     assertEquals("[null,null,null,null,null,null,null,null,null]", jsonArray.toString());
   }
 
-  public void testSameAddition() {
+  @Test
+  void testSameAddition() {
     JsonArray jsonArray = new JsonArray();
 
     jsonArray.add('a');
diff --git a/gson/src/test/java/com/google/gson/functional/JsonParserTest.java b/gson/src/test/java/com/google/gson/functional/JsonParserTest.java
index 965140ba08..81f499b21c 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonParserTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonParserTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
@@ -26,14 +29,13 @@
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.common.TestTypes.Nested;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.io.StringReader;
 import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for that use JsonParser and related Gson methods
@@ -41,23 +43,24 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class JsonParserTest extends TestCase {
+class JsonParserTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testParseInvalidJson() {
+  @Test
+  void testParseInvalidJson() {
     try {
       gson.fromJson("[[]", Object[].class);
       fail();
     } catch (JsonSyntaxException expected) { }
   }
 
-  public void testDeserializingCustomTree() {
+  @Test
+  void testDeserializingCustomTree() {
     JsonObject obj = new JsonObject();
     obj.addProperty("stringValue", "foo");
     obj.addProperty("intValue", 11);
@@ -66,7 +69,8 @@ public void testDeserializingCustomTree() {
     assertEquals("foo", target.stringValue);
   }
 
-  public void testBadTypeForDeserializingCustomTree() {
+  @Test
+  void testBadTypeForDeserializingCustomTree() {
     JsonObject obj = new JsonObject();
     obj.addProperty("stringValue", "foo");
     obj.addProperty("intValue", 11);
@@ -78,7 +82,8 @@ public void testBadTypeForDeserializingCustomTree() {
     } catch (JsonParseException expected) { }
   }
 
-  public void testBadFieldTypeForCustomDeserializerCustomTree() {
+  @Test
+  void testBadFieldTypeForCustomDeserializerCustomTree() {
     JsonArray array = new JsonArray();
     array.add(new JsonPrimitive("blah"));
     JsonObject obj = new JsonObject();
@@ -92,7 +97,8 @@ public void testBadFieldTypeForCustomDeserializerCustomTree() {
     } catch (JsonParseException expected) { }
   }
 
-  public void testBadFieldTypeForDeserializingCustomTree() {
+  @Test
+  void testBadFieldTypeForDeserializingCustomTree() {
     JsonArray array = new JsonArray();
     array.add(new JsonPrimitive("blah"));
     JsonObject primitive1 = new JsonObject();
@@ -109,7 +115,8 @@ public void testBadFieldTypeForDeserializingCustomTree() {
     } catch (JsonParseException expected) { }
   }
 
-  public void testChangingCustomTreeAndDeserializing() {
+  @Test
+  void testChangingCustomTreeAndDeserializing() {
     StringReader json =
       new StringReader("{'stringValue':'no message','intValue':10,'longValue':20}");
     JsonObject obj = (JsonObject) JsonParser.parseReader(json);
@@ -121,14 +128,16 @@ public void testChangingCustomTreeAndDeserializing() {
     assertEquals("fooBar", target.stringValue);
   }
 
-  public void testExtraCommasInArrays() {
+  @Test
+  void testExtraCommasInArrays() {
     Type type = new TypeToken<List<String>>() {}.getType();
     assertEquals(Arrays.asList("a", null, "b", null, null), gson.fromJson("[a,,b,,]", type));
     assertEquals(Arrays.asList(null, null), gson.fromJson("[,]", type));
     assertEquals(Arrays.asList("a", null), gson.fromJson("[a,]", type));
   }
 
-  public void testExtraCommasInMaps() {
+  @Test
+  void testExtraCommasInMaps() {
     Type type = new TypeToken<Map<String, String>>() {}.getType();
     try {
       gson.fromJson("{a:b,}", type);
diff --git a/gson/src/test/java/com/google/gson/functional/JsonTreeTest.java b/gson/src/test/java/com/google/gson/functional/JsonTreeTest.java
index a64794030a..a3b9000a03 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonTreeTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonTreeTest.java
@@ -1,5 +1,10 @@
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -8,7 +13,8 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for {@link Gson#toJsonTree(Object)} and 
@@ -17,16 +23,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class JsonTreeTest extends TestCase {
+class JsonTreeTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testToJsonTree() {
+  @Test
+  void testToJsonTree() {
     BagOfPrimitives bag = new BagOfPrimitives(10L, 5, false, "foo");
     JsonElement json = gson.toJsonTree(bag);
     assertTrue(json.isJsonObject());
@@ -39,7 +45,8 @@ public void testToJsonTree() {
     assertContains(obj, new JsonPrimitive("foo"));
   }
 
-  public void testToJsonTreeObjectType() {
+  @Test
+  void testToJsonTreeObjectType() {
     SubTypeOfBagOfPrimitives bag = new SubTypeOfBagOfPrimitives(10L, 5, false, "foo", 1.4F);
     JsonElement json = gson.toJsonTree(bag, BagOfPrimitives.class);
     assertTrue(json.isJsonObject());
@@ -52,7 +59,8 @@ public void testToJsonTreeObjectType() {
     assertContains(obj, new JsonPrimitive("foo"));
   }
 
-  public void testJsonTreeToString() {
+  @Test
+  void testJsonTreeToString() {
     SubTypeOfBagOfPrimitives bag = new SubTypeOfBagOfPrimitives(10L, 5, false, "foo", 1.4F);
     String json1 = gson.toJson(bag);
     JsonElement jsonElement = gson.toJsonTree(bag, SubTypeOfBagOfPrimitives.class);
@@ -60,7 +68,8 @@ public void testJsonTreeToString() {
     assertEquals(json1, json2);
   }
 
-  public void testJsonTreeNull() {
+  @Test
+  void testJsonTreeNull() {
     BagOfPrimitives bag = new BagOfPrimitives(10L, 5, false, null);
     JsonObject jsonElement = (JsonObject) gson.toJsonTree(bag, BagOfPrimitives.class);
     assertFalse(jsonElement.has("stringValue"));
@@ -77,7 +86,7 @@ private void assertContains(JsonObject json, JsonPrimitive child) {
     }
     fail();
   }
-  
+
   private static class SubTypeOfBagOfPrimitives extends BagOfPrimitives {
     @SuppressWarnings("unused")
     float f = 1.2F;
diff --git a/gson/src/test/java/com/google/gson/functional/LeniencyTest.java b/gson/src/test/java/com/google/gson/functional/LeniencyTest.java
index 6b5375e4b0..1d11c19ece 100644
--- a/gson/src/test/java/com/google/gson/functional/LeniencyTest.java
+++ b/gson/src/test/java/com/google/gson/functional/LeniencyTest.java
@@ -15,28 +15,30 @@
  */
 package com.google.gson.functional;
 
+import static java.util.Collections.singletonList;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.reflect.TypeToken;
 import java.util.List;
-import junit.framework.TestCase;
-
-import static java.util.Collections.singletonList;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for leniency option.
  */
-public class LeniencyTest extends TestCase {
+class LeniencyTest {
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder().setLenient().create();
   }
 
-  public void testLenientFromJson() {
+  @Test
+  void testLenientFromJson() {
     List<String> json = gson.fromJson(""
         + "[ # One!\n"
         + "  'Hi' #Element!\n"
diff --git a/gson/src/test/java/com/google/gson/functional/MapAsArrayTypeAdapterTest.java b/gson/src/test/java/com/google/gson/functional/MapAsArrayTypeAdapterTest.java
index 0d67ec8348..34b5ddb818 100644
--- a/gson/src/test/java/com/google/gson/functional/MapAsArrayTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/functional/MapAsArrayTypeAdapterTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonSyntaxException;
@@ -24,11 +27,13 @@
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
 
-public class MapAsArrayTypeAdapterTest extends TestCase {
+class MapAsArrayTypeAdapterTest {
 
-  public void testSerializeComplexMapWithTypeAdapter() {
+  @Test
+  void testSerializeComplexMapWithTypeAdapter() {
     Type type = new TypeToken<Map<Point, String>>() {}.getType();
     Gson gson = new GsonBuilder()
         .enableComplexMapKeySerialization()
@@ -53,7 +58,9 @@ public void testSerializeComplexMapWithTypeAdapter() {
         new TypeToken<Map<String, Boolean>>() {}.getType()));
   }
 
-  public void disabled_testTwoTypesCollapseToOneSerialize() {
+  @Disabled
+  @Test
+  void testTwoTypesCollapseToOneSerialize() {
     Gson gson = new GsonBuilder()
         .enableComplexMapKeySerialization()
         .create();
@@ -68,7 +75,8 @@ public void disabled_testTwoTypesCollapseToOneSerialize() {
     }
   }
 
-  public void testTwoTypesCollapseToOneDeserialize() {
+  @Test
+  void testTwoTypesCollapseToOneDeserialize() {
     Gson gson = new GsonBuilder()
         .enableComplexMapKeySerialization()
         .create();
@@ -81,7 +89,8 @@ public void testTwoTypesCollapseToOneDeserialize() {
     }
   }
 
-  public void testMultipleEnableComplexKeyRegistrationHasNoEffect() throws Exception {
+  @Test
+  void testMultipleEnableComplexKeyRegistrationHasNoEffect() throws Exception {
     Type type = new TypeToken<Map<Point, String>>() {}.getType();
     Gson gson = new GsonBuilder()
         .enableComplexMapKeySerialization()
@@ -96,7 +105,8 @@ public void testMultipleEnableComplexKeyRegistrationHasNoEffect() throws Excepti
     assertEquals(original, gson.<Map<Point, String>>fromJson(json, type));
   }
 
-  public void testMapWithTypeVariableSerialization() {
+  @Test
+  void testMapWithTypeVariableSerialization() {
     Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
     PointWithProperty<Point> map = new PointWithProperty<Point>();
     map.map.put(new Point(2, 3), new Point(4, 5));
@@ -105,7 +115,8 @@ public void testMapWithTypeVariableSerialization() {
     assertEquals("{\"map\":[[{\"x\":2,\"y\":3},{\"x\":4,\"y\":5}]]}", json);
   }
 
-  public void testMapWithTypeVariableDeserialization() {
+  @Test
+  void testMapWithTypeVariableDeserialization() {
     Gson gson = new GsonBuilder().enableComplexMapKeySerialization().create();
     String json = "{map:[[{x:2,y:3},{x:4,y:5}]]}";
     Type type = new TypeToken<PointWithProperty<Point>>(){}.getType();
diff --git a/gson/src/test/java/com/google/gson/functional/MapTest.java b/gson/src/test/java/com/google/gson/functional/MapTest.java
index d14585b382..e172d75d5f 100644
--- a/gson/src/test/java/com/google/gson/functional/MapTest.java
+++ b/gson/src/test/java/com/google/gson/functional/MapTest.java
@@ -16,17 +16,11 @@
 
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.LinkedHashMap;
-import java.util.Map;
-import java.util.SortedMap;
-import java.util.TreeMap;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-import java.util.concurrent.ConcurrentNavigableMap;
-import java.util.concurrent.ConcurrentSkipListMap;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -42,8 +36,19 @@
 import com.google.gson.common.TestTypes;
 import com.google.gson.internal.$Gson$Types;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
+import java.lang.reflect.Type;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ConcurrentSkipListMap;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional test for Json serialization and deserialization for Maps
@@ -51,16 +56,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class MapTest extends TestCase {
+class MapTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testMapSerialization() {
+  @Test
+  void testMapSerialization() {
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     map.put("a", 1);
     map.put("b", 2);
@@ -70,7 +75,8 @@ public void testMapSerialization() {
     assertTrue(json.contains("\"b\":2"));
   }
 
-  public void testMapDeserialization() {
+  @Test
+  void testMapDeserialization() {
     String json = "{\"a\":1,\"b\":2}";
     Type typeOfMap = new TypeToken<Map<String,Integer>>(){}.getType();
     Map<String, Integer> target = gson.fromJson(json, typeOfMap);
@@ -79,7 +85,8 @@ public void testMapDeserialization() {
   }
 
   @SuppressWarnings({"unchecked", "rawtypes"})
-  public void testRawMapSerialization() {
+  @Test
+  void testRawMapSerialization() {
     Map map = new LinkedHashMap();
     map.put("a", 1);
     map.put("b", "string");
@@ -88,20 +95,23 @@ public void testRawMapSerialization() {
     assertTrue(json.contains("\"b\":\"string\""));
   }
 
-  public void testMapSerializationEmpty() {
+  @Test
+  void testMapSerializationEmpty() {
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
     String json = gson.toJson(map, typeOfMap);
     assertEquals("{}", json);
   }
 
-  public void testMapDeserializationEmpty() {
+  @Test
+  void testMapDeserializationEmpty() {
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
     Map<String, Integer> map = gson.fromJson("{}", typeOfMap);
     assertTrue(map.isEmpty());
   }
 
-  public void testMapSerializationWithNullValue() {
+  @Test
+  void testMapSerializationWithNullValue() {
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     map.put("abc", null);
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
@@ -111,14 +121,16 @@ public void testMapSerializationWithNullValue() {
     assertEquals("{}", json);
   }
 
-  public void testMapDeserializationWithNullValue() {
+  @Test
+  void testMapDeserializationWithNullValue() {
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
     Map<String, Integer> map = gson.fromJson("{\"abc\":null}", typeOfMap);
     assertEquals(1, map.size());
     assertNull(map.get("abc"));
   }
 
-  public void testMapSerializationWithNullValueButSerializeNulls() {
+  @Test
+  void testMapSerializationWithNullValueButSerializeNulls() {
     gson = new GsonBuilder().serializeNulls().create();
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     map.put("abc", null);
@@ -128,7 +140,8 @@ public void testMapSerializationWithNullValueButSerializeNulls() {
     assertEquals("{\"abc\":null}", json);
   }
 
-  public void testMapSerializationWithNullKey() {
+  @Test
+  void testMapSerializationWithNullKey() {
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     map.put(null, 123);
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
@@ -137,7 +150,8 @@ public void testMapSerializationWithNullKey() {
     assertEquals("{\"null\":123}", json);
   }
 
-  public void testMapDeserializationWithNullKey() {
+  @Test
+  void testMapDeserializationWithNullKey() {
     Type typeOfMap = new TypeToken<Map<String, Integer>>() {}.getType();
     Map<String, Integer> map = gson.fromJson("{\"null\":123}", typeOfMap);
     assertEquals(1, map.size());
@@ -150,7 +164,8 @@ public void testMapDeserializationWithNullKey() {
     assertNull(map.get(null));
   }
 
-  public void testMapSerializationWithIntegerKeys() {
+  @Test
+  void testMapSerializationWithIntegerKeys() {
     Map<Integer, String> map = new LinkedHashMap<Integer, String>();
     map.put(123, "456");
     Type typeOfMap = new TypeToken<Map<Integer, String>>() {}.getType();
@@ -159,7 +174,8 @@ public void testMapSerializationWithIntegerKeys() {
     assertEquals("{\"123\":\"456\"}", json);
   }
 
-  public void testMapDeserializationWithIntegerKeys() {
+  @Test
+  void testMapDeserializationWithIntegerKeys() {
     Type typeOfMap = new TypeToken<Map<Integer, String>>() {}.getType();
     Map<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -167,7 +183,8 @@ public void testMapDeserializationWithIntegerKeys() {
     assertEquals("456", map.get(123));
   }
 
-  public void testMapDeserializationWithUnquotedIntegerKeys() {
+  @Test
+  void testMapDeserializationWithUnquotedIntegerKeys() {
     Type typeOfMap = new TypeToken<Map<Integer, String>>() {}.getType();
     Map<Integer, String> map = gson.fromJson("{123:\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -175,7 +192,8 @@ public void testMapDeserializationWithUnquotedIntegerKeys() {
     assertEquals("456", map.get(123));
   }
 
-  public void testMapDeserializationWithLongKeys() {
+  @Test
+  void testMapDeserializationWithLongKeys() {
     long longValue = 9876543210L;
     String json = String.format("{\"%d\":\"456\"}", longValue);
     Type typeOfMap = new TypeToken<Map<Long, String>>() {}.getType();
@@ -185,7 +203,8 @@ public void testMapDeserializationWithLongKeys() {
     assertEquals("456", map.get(longValue));
   }
 
-  public void testMapDeserializationWithUnquotedLongKeys() {
+  @Test
+  void testMapDeserializationWithUnquotedLongKeys() {
     long longKey = 9876543210L;
     String json = String.format("{%d:\"456\"}", longKey);
     Type typeOfMap = new TypeToken<Map<Long, String>>() {}.getType();
@@ -195,7 +214,8 @@ public void testMapDeserializationWithUnquotedLongKeys() {
     assertEquals("456", map.get(longKey));
   }
 
-  public void testHashMapDeserialization() throws Exception {
+  @Test
+  void testHashMapDeserialization() throws Exception {
     Type typeOfMap = new TypeToken<HashMap<Integer, String>>() {}.getType();
     HashMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -203,7 +223,8 @@ public void testHashMapDeserialization() throws Exception {
     assertEquals("456", map.get(123));
   }
 
-  public void testSortedMap() throws Exception {
+  @Test
+  void testSortedMap() throws Exception {
     Type typeOfMap = new TypeToken<SortedMap<Integer, String>>() {}.getType();
     SortedMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -211,7 +232,8 @@ public void testSortedMap() throws Exception {
     assertEquals("456", map.get(123));
   }
 
-  public void testConcurrentMap() throws Exception {
+  @Test
+  void testConcurrentMap() throws Exception {
     Type typeOfMap = new TypeToken<ConcurrentMap<Integer, String>>() {}.getType();
     ConcurrentMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -221,7 +243,8 @@ public void testConcurrentMap() throws Exception {
     assertEquals("{\"123\":\"456\"}", json);
   }
 
-  public void testConcurrentHashMap() throws Exception {
+  @Test
+  void testConcurrentHashMap() throws Exception {
     Type typeOfMap = new TypeToken<ConcurrentHashMap<Integer, String>>() {}.getType();
     ConcurrentHashMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -231,7 +254,8 @@ public void testConcurrentHashMap() throws Exception {
     assertEquals("{\"123\":\"456\"}", json);
   }
 
-  public void testConcurrentNavigableMap() throws Exception {
+  @Test
+  void testConcurrentNavigableMap() throws Exception {
     Type typeOfMap = new TypeToken<ConcurrentNavigableMap<Integer, String>>() {}.getType();
     ConcurrentNavigableMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -241,7 +265,8 @@ public void testConcurrentNavigableMap() throws Exception {
     assertEquals("{\"123\":\"456\"}", json);
   }
 
-  public void testConcurrentSkipListMap() throws Exception {
+  @Test
+  void testConcurrentSkipListMap() throws Exception {
     Type typeOfMap = new TypeToken<ConcurrentSkipListMap<Integer, String>>() {}.getType();
     ConcurrentSkipListMap<Integer, String> map = gson.fromJson("{\"123\":\"456\"}", typeOfMap);
     assertEquals(1, map.size());
@@ -251,7 +276,8 @@ public void testConcurrentSkipListMap() throws Exception {
     assertEquals("{\"123\":\"456\"}", json);
   }
 
-  public void testParameterizedMapSubclassSerialization() {
+  @Test
+  void testParameterizedMapSubclassSerialization() {
     MyParameterizedMap<String, String> map = new MyParameterizedMap<String, String>(10);
     map.put("a", "b");
     Type type = new TypeToken<MyParameterizedMap<String, String>>() {}.getType();
@@ -267,14 +293,16 @@ private static class MyParameterizedMap<K, V> extends LinkedHashMap<K, V> {
     }
   }
 
-  public void testMapSubclassSerialization() {
+  @Test
+  void testMapSubclassSerialization() {
     MyMap map = new MyMap();
     map.put("a", "b");
     String json = gson.toJson(map, MyMap.class);
     assertTrue(json.contains("\"a\":\"b\""));
   }
 
-  public void testMapStandardSubclassDeserialization() {
+  @Test
+  void testMapStandardSubclassDeserialization() {
     String json = "{a:'1',b:'2'}";
     Type type = new TypeToken<LinkedHashMap<String, String>>() {}.getType();
     LinkedHashMap<String, Integer> map = gson.fromJson(json, type);
@@ -282,8 +310,10 @@ public void testMapStandardSubclassDeserialization() {
     assertEquals("2", map.get("b"));
   }
 
-  public void testMapSubclassDeserialization() {
+  @Test
+  void testMapSubclassDeserialization() {
     Gson gson = new GsonBuilder().registerTypeAdapter(MyMap.class, new InstanceCreator<MyMap>() {
+      @Override
       public MyMap createInstance(Type type) {
         return new MyMap();
       }
@@ -294,11 +324,13 @@ public MyMap createInstance(Type type) {
     assertEquals("2", map.get("b"));
   }
 
-  public void testCustomSerializerForSpecificMapType() {
+  @Test
+  void testCustomSerializerForSpecificMapType() {
     Type type = $Gson$Types.newParameterizedTypeWithOwner(
         null, Map.class, String.class, Long.class);
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(type, new JsonSerializer<Map<String, Long>>() {
+          @Override
           public JsonElement serialize(Map<String, Long> src, Type typeOfSrc,
               JsonSerializationContext context) {
             JsonArray array = new JsonArray();
@@ -327,7 +359,8 @@ private static class ClassWithAMap {
   /**
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=99
    */
-  public void testMapSerializationWithNullValues() {
+  @Test
+  void testMapSerializationWithNullValues() {
     ClassWithAMap target = new ClassWithAMap();
     target.map.put("name1", null);
     target.map.put("name2", "value2");
@@ -339,7 +372,8 @@ public void testMapSerializationWithNullValues() {
   /**
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=99
    */
-  public void testMapSerializationWithNullValuesSerialized() {
+  @Test
+  void testMapSerializationWithNullValuesSerialized() {
     Gson gson = new GsonBuilder().serializeNulls().create();
     ClassWithAMap target = new ClassWithAMap();
     target.map.put("name1", null);
@@ -349,7 +383,8 @@ public void testMapSerializationWithNullValuesSerialized() {
     assertTrue(json.contains("name2"));
   }
 
-  public void testMapSerializationWithWildcardValues() {
+  @Test
+  void testMapSerializationWithWildcardValues() {
     Map<String, ? extends Collection<? extends Integer>> map =
         new LinkedHashMap<String, Collection<Integer>>();
     map.put("test", null);
@@ -360,7 +395,8 @@ public void testMapSerializationWithWildcardValues() {
     assertEquals("{}", json);
   }
 
-  public void testMapDeserializationWithWildcardValues() {
+  @Test
+  void testMapDeserializationWithWildcardValues() {
     Type typeOfMap = new TypeToken<Map<String, ? extends Long>>() {}.getType();
     Map<String, ? extends Long> map = gson.fromJson("{\"test\":123}", typeOfMap);
     assertEquals(1, map.size());
@@ -378,7 +414,8 @@ private static class MyMap extends LinkedHashMap<String, String> {
   /**
    * From bug report http://code.google.com/p/google-gson/issues/detail?id=95
    */
-  public void testMapOfMapSerialization() {
+  @Test
+  void testMapOfMapSerialization() {
     Map<String, Map<String, String>> map = new HashMap<String, Map<String, String>>();
     Map<String, String> nestedMap = new HashMap<String, String>();
     nestedMap.put("1", "1");
@@ -393,7 +430,8 @@ public void testMapOfMapSerialization() {
   /**
    * From bug report http://code.google.com/p/google-gson/issues/detail?id=95
    */
-  public void testMapOfMapDeserialization() {
+  @Test
+  void testMapOfMapDeserialization() {
     String json = "{nestedMap:{'2':'2','1':'1'}}";
     Type type = new TypeToken<Map<String, Map<String, String>>>(){}.getType();
     Map<String, Map<String, String>> map = gson.fromJson(json, type);
@@ -405,7 +443,8 @@ public void testMapOfMapDeserialization() {
   /**
    * From bug report http://code.google.com/p/google-gson/issues/detail?id=178
    */
-  public void testMapWithQuotes() {
+  @Test
+  void testMapWithQuotes() {
     Map<String, String> map = new HashMap<String, String>();
     map.put("a\"b", "c\"d");
     String json = gson.toJson(map);
@@ -415,14 +454,16 @@ public void testMapWithQuotes() {
   /**
    * From issue 227.
    */
-  public void testWriteMapsWithEmptyStringKey() {
+  @Test
+  void testWriteMapsWithEmptyStringKey() {
     Map<String, Boolean> map = new HashMap<String, Boolean>();
     map.put("", true);
     assertEquals("{\"\":true}", gson.toJson(map));
 
   }
 
-  public void testReadMapsWithEmptyStringKey() {
+  @Test
+  void testReadMapsWithEmptyStringKey() {
     Map<String, Boolean> map = gson.fromJson("{\"\":true}", new TypeToken<Map<String, Boolean>>() {}.getType());
     assertEquals(Boolean.TRUE, map.get(""));
   }
@@ -430,7 +471,8 @@ public void testReadMapsWithEmptyStringKey() {
   /**
    * From bug report http://code.google.com/p/google-gson/issues/detail?id=204
    */
-  public void testSerializeMaps() {
+  @Test
+  void testSerializeMaps() {
     Map<String, Object> map = new LinkedHashMap<String, Object>();
     map.put("a", 12);
     map.put("b", null);
@@ -443,8 +485,8 @@ public void testSerializeMaps() {
     assertEquals("{\"a\":12,\"b\":null,\"c\":{\"test\":1,\"TestStringArray\":[\"one\",\"two\"]}}",
         new GsonBuilder().serializeNulls().create().toJson(map));
     assertEquals("{\n  \"a\": 12,\n  \"b\": null,\n  \"c\": "
-  		+ "{\n    \"test\": 1,\n    \"TestStringArray\": "
-  		+ "[\n      \"one\",\n      \"two\"\n    ]\n  }\n}",
+        + "{\n    \"test\": 1,\n    \"TestStringArray\": "
+        + "[\n      \"one\",\n      \"two\"\n    ]\n  }\n}",
         new GsonBuilder().setPrettyPrinting().serializeNulls().create().toJson(map));
     assertEquals("{\"a\":12,\"c\":{\"test\":1,\"TestStringArray\":[\"one\",\"two\"]}}",
         new GsonBuilder().create().toJson(map));
@@ -458,7 +500,8 @@ public void testSerializeMaps() {
         new Gson().toJson(map));
   }
 
-  public final void testInterfaceTypeMap() {
+  @Test
+  void testInterfaceTypeMap() {
     MapClass element = new MapClass();
     TestTypes.Sub subType = new TestTypes.Sub();
     element.addBase("Test", subType);
@@ -479,7 +522,8 @@ public final void testInterfaceTypeMap() {
     assertEquals(expected, json);
   }
 
-  public final void testInterfaceTypeMapWithSerializer() {
+  @Test
+  void testInterfaceTypeMapWithSerializer() {
     MapClass element = new MapClass();
     TestTypes.Sub subType = new TestTypes.Sub();
     element.addBase("Test", subType);
@@ -493,6 +537,7 @@ public final void testInterfaceTypeMapWithSerializer() {
         + "\"subs\":{\"Test\":" + subTypeJson + "}}";
 
     JsonSerializer<TestTypes.Base> baseTypeAdapter = new JsonSerializer<TestTypes.Base>() {
+      @Override
       public JsonElement serialize(TestTypes.Base src, Type typeOfSrc,
           JsonSerializationContext context) {
         return baseTypeJsonElement;
@@ -513,7 +558,8 @@ public JsonElement serialize(TestTypes.Base src, Type typeOfSrc,
     assertEquals(expected, json);
   }
 
-  public void testGeneralMapField() throws Exception {
+  @Test
+  void testGeneralMapField() throws Exception {
     MapWithGeneralMapParameters map = new MapWithGeneralMapParameters();
     map.map.put("string", "testString");
     map.map.put("stringArray", new String[]{"one", "two"});
@@ -529,7 +575,8 @@ public void testGeneralMapField() throws Exception {
     assertEquals(expected, gson.toJson(map));
   }
 
-  public void testComplexKeysSerialization() {
+  @Test
+  void testComplexKeysSerialization() {
     Map<Point, String> map = new LinkedHashMap<Point, String>();
     map.put(new Point(2, 3), "a");
     map.put(new Point(5, 7), "b");
@@ -538,7 +585,8 @@ public void testComplexKeysSerialization() {
     assertEquals(json, gson.toJson(map, Map.class));
   }
 
-  public void testComplexKeysDeserialization() {
+  @Test
+  void testComplexKeysDeserialization() {
     String json = "{'2,3':'a','5,7':'b'}";
     try {
       gson.fromJson(json, new TypeToken<Map<Point, String>>() {}.getType());
@@ -547,7 +595,8 @@ public void testComplexKeysDeserialization() {
     }
   }
 
-  public void testStringKeyDeserialization() {
+  @Test
+  void testStringKeyDeserialization() {
     String json = "{'2,3':'a','5,7':'b'}";
     Map<String, String> map = new LinkedHashMap<String, String>();
     map.put("2,3", "a");
@@ -555,7 +604,8 @@ public void testStringKeyDeserialization() {
     assertEquals(map, gson.fromJson(json, new TypeToken<Map<String, String>>() {}.getType()));
   }
 
-  public void testNumberKeyDeserialization() {
+  @Test
+  void testNumberKeyDeserialization() {
     String json = "{'2.3':'a','5.7':'b'}";
     Map<Double, String> map = new LinkedHashMap<Double, String>();
     map.put(2.3, "a");
@@ -563,7 +613,8 @@ public void testNumberKeyDeserialization() {
     assertEquals(map, gson.fromJson(json, new TypeToken<Map<Double, String>>() {}.getType()));
   }
 
-  public void testBooleanKeyDeserialization() {
+  @Test
+  void testBooleanKeyDeserialization() {
     String json = "{'true':'a','false':'b'}";
     Map<Boolean, String> map = new LinkedHashMap<Boolean, String>();
     map.put(true, "a");
@@ -571,7 +622,8 @@ public void testBooleanKeyDeserialization() {
     assertEquals(map, gson.fromJson(json, new TypeToken<Map<Boolean, String>>() {}.getType()));
   }
 
-  public void testMapDeserializationWithDuplicateKeys() {
+  @Test
+  void testMapDeserializationWithDuplicateKeys() {
     try {
       gson.fromJson("{'a':1,'a':2}", new TypeToken<Map<String, Integer>>() {}.getType());
       fail();
@@ -579,7 +631,8 @@ public void testMapDeserializationWithDuplicateKeys() {
     }
   }
 
-  public void testSerializeMapOfMaps() {
+  @Test
+  void testSerializeMapOfMaps() {
     Type type = new TypeToken<Map<String, Map<String, String>>>() {}.getType();
     Map<String, Map<String, String>> map = newMap(
         "a", newMap("ka1", "va1", "ka2", "va2"),
@@ -588,7 +641,8 @@ public void testSerializeMapOfMaps() {
         gson.toJson(map, type).replace('"', '\''));
   }
 
-  public void testDeerializeMapOfMaps() {
+  @Test
+  void testDeerializeMapOfMaps() {
     Type type = new TypeToken<Map<String, Map<String, String>>>() {}.getType();
     Map<String, Map<String, String>> map = newMap(
         "a", newMap("ka1", "va1", "ka2", "va2"),
@@ -604,7 +658,8 @@ private <K, V> Map<K, V> newMap(K key1, V value1, K key2, V value2) {
     return result;
   }
 
-  public void testMapNamePromotionWithJsonElementReader() {
+  @Test
+  void testMapNamePromotionWithJsonElementReader() {
     String json = "{'2.3':'a'}";
     Map<Double, String> map = new LinkedHashMap<Double, String>();
     map.put(2.3, "a");
diff --git a/gson/src/test/java/com/google/gson/functional/MoreSpecificTypeSerializationTest.java b/gson/src/test/java/com/google/gson/functional/MoreSpecificTypeSerializationTest.java
index 7ecbffc841..a66e62447e 100644
--- a/gson/src/test/java/com/google/gson/functional/MoreSpecificTypeSerializationTest.java
+++ b/gson/src/test/java/com/google/gson/functional/MoreSpecificTypeSerializationTest.java
@@ -16,15 +16,19 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.JsonObject;
-
-import junit.framework.TestCase;
-
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Tests for Gson serialization of a sub-class object while encountering a base-class type
@@ -32,33 +36,35 @@
  * @author Inderjeet Singh
  */
 @SuppressWarnings("unused")
-public class MoreSpecificTypeSerializationTest extends TestCase {
+class MoreSpecificTypeSerializationTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testSubclassFields() {
+  @Test
+  void testSubclassFields() {
     ClassWithBaseFields target = new ClassWithBaseFields(new Sub(1, 2));
     String json = gson.toJson(target);
     assertTrue(json.contains("\"b\":1"));
     assertTrue(json.contains("\"s\":2"));
   }
 
-  public void testListOfSubclassFields() {
+  @Test
+  void testListOfSubclassFields() {
     Collection<Base> list = new ArrayList<Base>();
     list.add(new Base(1));
     list.add(new Sub(2, 3));
     ClassWithContainersOfBaseFields target = new ClassWithContainersOfBaseFields(list, null);
     String json = gson.toJson(target);
-    assertTrue(json, json.contains("{\"b\":1}"));
-    assertTrue(json, json.contains("{\"s\":3,\"b\":2}"));
+    assertTrue(json.contains("{\"b\":1}"), json);
+    assertTrue(json.contains("{\"s\":3,\"b\":2}"), json);
   }
 
-  public void testMapOfSubclassFields() {
+  @Test
+  void testMapOfSubclassFields() {
     Map<String, Base> map = new HashMap<String, Base>();
     map.put("base", new Base(1));
     map.put("sub", new Sub(2, 3));
@@ -73,7 +79,8 @@ public void testMapOfSubclassFields() {
   /**
    * For parameterized type, Gson ignores the more-specific type and sticks to the declared type
    */
-  public void testParameterizedSubclassFields() {
+  @Test
+  void testParameterizedSubclassFields() {
     ClassWithParameterizedBaseFields target = new ClassWithParameterizedBaseFields(
         new ParameterizedSub<String>("one", "two"));
     String json = gson.toJson(target);
@@ -85,22 +92,24 @@ public void testParameterizedSubclassFields() {
    * For parameterized type in a List, Gson ignores the more-specific type and sticks to
    * the declared type
    */
-  public void testListOfParameterizedSubclassFields() {
+  @Test
+  void testListOfParameterizedSubclassFields() {
     Collection<ParameterizedBase<String>> list = new ArrayList<ParameterizedBase<String>>();
     list.add(new ParameterizedBase<String>("one"));
     list.add(new ParameterizedSub<String>("two", "three"));
     ClassWithContainersOfParameterizedBaseFields target =
       new ClassWithContainersOfParameterizedBaseFields(list, null);
     String json = gson.toJson(target);
-    assertTrue(json, json.contains("{\"t\":\"one\"}"));
-    assertFalse(json, json.contains("\"s\":"));
+    assertTrue(json.contains("{\"t\":\"one\"}"), json);
+    assertFalse(json.contains("\"s\":"), json);
   }
 
   /**
    * For parameterized type in a map, Gson ignores the more-specific type and sticks to the
    * declared type
    */
-  public void testMapOfParameterizedSubclassFields() {
+  @Test
+  void testMapOfParameterizedSubclassFields() {
     Map<String, ParameterizedBase<String>> map = new HashMap<String, ParameterizedBase<String>>();
     map.put("base", new ParameterizedBase<String>("one"));
     map.put("sub", new ParameterizedSub<String>("two", "three"));
diff --git a/gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java b/gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java
index ab76e64918..abd158de29 100644
--- a/gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java
+++ b/gson/src/test/java/com/google/gson/functional/NamingPolicyTest.java
@@ -15,6 +15,9 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.FieldNamingPolicy;
 import com.google.gson.FieldNamingStrategy;
 import com.google.gson.Gson;
@@ -22,10 +25,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.google.gson.common.TestTypes.ClassWithSerializedNameFields;
 import com.google.gson.common.TestTypes.StringWrapper;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.Field;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for naming policies.
@@ -33,58 +35,64 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class NamingPolicyTest extends TestCase {
+class NamingPolicyTest {
   private GsonBuilder builder;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     builder = new GsonBuilder();
   }
 
-  public void testGsonWithNonDefaultFieldNamingPolicySerialization() {
+  @Test
+  void testGsonWithNonDefaultFieldNamingPolicySerialization() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE).create();
     StringWrapper target = new StringWrapper("blah");
     assertEquals("{\"SomeConstantStringInstanceField\":\""
         + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithNonDefaultFieldNamingPolicyDeserialiation() {
+  @Test
+  void testGsonWithNonDefaultFieldNamingPolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE).create();
     String target = "{\"SomeConstantStringInstanceField\":\"someValue\"}";
     StringWrapper deserializedObject = gson.fromJson(target, StringWrapper.class);
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testGsonWithLowerCaseDashPolicySerialization() {
+  @Test
+  void testGsonWithLowerCaseDashPolicySerialization() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_DASHES).create();
     StringWrapper target = new StringWrapper("blah");
     assertEquals("{\"some-constant-string-instance-field\":\""
         + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithLowerCaseDotPolicySerialization() {
+  @Test
+  void testGsonWithLowerCaseDotPolicySerialization() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_DOTS).create();
     StringWrapper target = new StringWrapper("blah");
     assertEquals("{\"some.constant.string.instance.field\":\""
           + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithLowerCaseDotPolicyDeserialiation() {
+  @Test
+  void testGsonWithLowerCaseDotPolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_DOTS).create();
     String target = "{\"some.constant.string.instance.field\":\"someValue\"}";
     StringWrapper deserializedObject = gson.fromJson(target, StringWrapper.class);
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testGsonWithLowerCaseDashPolicyDeserialiation() {
+  @Test
+  void testGsonWithLowerCaseDashPolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_DASHES).create();
     String target = "{\"some-constant-string-instance-field\":\"someValue\"}";
     StringWrapper deserializedObject = gson.fromJson(target, StringWrapper.class);
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testGsonWithLowerCaseUnderscorePolicySerialization() {
+  @Test
+  void testGsonWithLowerCaseUnderscorePolicySerialization() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
         .create();
     StringWrapper target = new StringWrapper("blah");
@@ -92,7 +100,8 @@ public void testGsonWithLowerCaseUnderscorePolicySerialization() {
         + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithLowerCaseUnderscorePolicyDeserialiation() {
+  @Test
+  void testGsonWithLowerCaseUnderscorePolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
         .create();
     String target = "{\"some_constant_string_instance_field\":\"someValue\"}";
@@ -100,14 +109,16 @@ public void testGsonWithLowerCaseUnderscorePolicyDeserialiation() {
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testGsonWithSerializedNameFieldNamingPolicySerialization() {
+  @Test
+  void testGsonWithSerializedNameFieldNamingPolicySerialization() {
     Gson gson = builder.create();
     ClassWithSerializedNameFields expected = new ClassWithSerializedNameFields(5, 6);
     String actual = gson.toJson(expected);
     assertEquals(expected.getExpectedJson(), actual);
   }
 
-  public void testGsonWithSerializedNameFieldNamingPolicyDeserialization() {
+  @Test
+  void testGsonWithSerializedNameFieldNamingPolicyDeserialization() {
     Gson gson = builder.create();
     ClassWithSerializedNameFields expected = new ClassWithSerializedNameFields(5, 7);
     ClassWithSerializedNameFields actual =
@@ -115,7 +126,8 @@ public void testGsonWithSerializedNameFieldNamingPolicyDeserialization() {
     assertEquals(expected.f, actual.f);
   }
 
-  public void testGsonDuplicateNameUsingSerializedNameFieldNamingPolicySerialization() {
+  @Test
+  void testGsonDuplicateNameUsingSerializedNameFieldNamingPolicySerialization() {
     Gson gson = builder.create();
     try {
       ClassWithDuplicateFields target = new ClassWithDuplicateFields(10);
@@ -125,7 +137,8 @@ public void testGsonDuplicateNameUsingSerializedNameFieldNamingPolicySerializati
     }
   }
 
-  public void testGsonWithUpperCamelCaseSpacesPolicySerialiation() {
+  @Test
+  void testGsonWithUpperCamelCaseSpacesPolicySerialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES)
         .create();
     StringWrapper target = new StringWrapper("blah");
@@ -133,7 +146,8 @@ public void testGsonWithUpperCamelCaseSpacesPolicySerialiation() {
         + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithUpperCamelCaseSpacesPolicyDeserialiation() {
+  @Test
+  void testGsonWithUpperCamelCaseSpacesPolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES)
         .create();
     String target = "{\"Some Constant String Instance Field\":\"someValue\"}";
@@ -141,7 +155,8 @@ public void testGsonWithUpperCamelCaseSpacesPolicyDeserialiation() {
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testGsonWithUpperCaseUnderscorePolicySerialization() {
+  @Test
+  void testGsonWithUpperCaseUnderscorePolicySerialization() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CASE_WITH_UNDERSCORES)
         .create();
     StringWrapper target = new StringWrapper("blah");
@@ -149,7 +164,8 @@ public void testGsonWithUpperCaseUnderscorePolicySerialization() {
         + target.someConstantStringInstanceField + "\"}", gson.toJson(target));
   }
 
-  public void testGsonWithUpperCaseUnderscorePolicyDeserialiation() {
+  @Test
+  void testGsonWithUpperCaseUnderscorePolicyDeserialiation() {
     Gson gson = builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CASE_WITH_UNDERSCORES)
         .create();
     String target = "{\"SOME_CONSTANT_STRING_INSTANCE_FIELD\":\"someValue\"}";
@@ -157,14 +173,16 @@ public void testGsonWithUpperCaseUnderscorePolicyDeserialiation() {
     assertEquals("someValue", deserializedObject.someConstantStringInstanceField);
   }
 
-  public void testDeprecatedNamingStrategy() throws Exception {
+  @Test
+  void testDeprecatedNamingStrategy() throws Exception {
     Gson gson = builder.setFieldNamingStrategy(new UpperCaseNamingStrategy()).create();
     ClassWithDuplicateFields target = new ClassWithDuplicateFields(10);
     String actual = gson.toJson(target);
     assertEquals("{\"A\":10}", actual);
   }
 
-  public void testComplexFieldNameStrategy() throws Exception {
+  @Test
+  void testComplexFieldNameStrategy() throws Exception {
     Gson gson = new Gson();
     String json = gson.toJson(new ClassWithComplexFieldName(10));
     String escapedFieldName = "@value\\\"_s$\\\\";
@@ -175,7 +193,8 @@ public void testComplexFieldNameStrategy() throws Exception {
   }
 
   /** http://code.google.com/p/google-gson/issues/detail?id=349 */
-  public void testAtSignInSerializedName() {
+  @Test
+  void testAtSignInSerializedName() {
     assertEquals("{\"@foo\":\"bar\"}", new Gson().toJson(new AtName()));
   }
 
diff --git a/gson/src/test/java/com/google/gson/functional/NullObjectAndFieldTest.java b/gson/src/test/java/com/google/gson/functional/NullObjectAndFieldTest.java
index a9b77f1d80..90f1ad1cee 100644
--- a/gson/src/test/java/com/google/gson/functional/NullObjectAndFieldTest.java
+++ b/gson/src/test/java/com/google/gson/functional/NullObjectAndFieldTest.java
@@ -16,22 +16,26 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonNull;
 import com.google.gson.JsonObject;
-import com.google.gson.JsonDeserializationContext;
-import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.common.TestTypes.ClassWithObjects;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.Type;
 import java.util.Collection;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the different cases for serializing (or ignoring) null fields and object.
@@ -39,16 +43,16 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class NullObjectAndFieldTest extends TestCase {
+class NullObjectAndFieldTest {
   private GsonBuilder gsonBuilder;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gsonBuilder = new GsonBuilder().serializeNulls();
   }
 
-  public void testTopLevelNullObjectSerialization() {
+  @Test
+  void testTopLevelNullObjectSerialization() {
     Gson gson = gsonBuilder.create();
     String actual = gson.toJson(null);
     assertEquals("null", actual);
@@ -57,13 +61,15 @@ public void testTopLevelNullObjectSerialization() {
     assertEquals("null", actual);
   }
 
-  public void testTopLevelNullObjectDeserialization() throws Exception {
+  @Test
+  void testTopLevelNullObjectDeserialization() throws Exception {
     Gson gson = gsonBuilder.create();
     String actual = gson.fromJson("null", String.class);
     assertNull(actual);
   }
 
-  public void testExplicitSerializationOfNulls() {
+  @Test
+  void testExplicitSerializationOfNulls() {
     Gson gson = gsonBuilder.create();
     ClassWithObjects target = new ClassWithObjects(null);
     String actual = gson.toJson(target);
@@ -71,54 +77,61 @@ public void testExplicitSerializationOfNulls() {
     assertEquals(expected, actual);
   }
 
-  public void testExplicitDeserializationOfNulls() throws Exception {
+  @Test
+  void testExplicitDeserializationOfNulls() throws Exception {
     Gson gson = gsonBuilder.create();
     ClassWithObjects target = gson.fromJson("{\"bag\":null}", ClassWithObjects.class);
     assertNull(target.bag);
   }
-  
-  public void testExplicitSerializationOfNullArrayMembers() {
+
+  @Test
+  void testExplicitSerializationOfNullArrayMembers() {
     Gson gson = gsonBuilder.create();
     ClassWithMembers target = new ClassWithMembers();
     String json = gson.toJson(target);
     assertTrue(json.contains("\"array\":null"));
   }
-  
-  /** 
+
+  /**
    * Added to verify http://code.google.com/p/google-gson/issues/detail?id=68
    */
-  public void testNullWrappedPrimitiveMemberSerialization() {
+  @Test
+  void testNullWrappedPrimitiveMemberSerialization() {
     Gson gson = gsonBuilder.serializeNulls().create();
     ClassWithNullWrappedPrimitive target = new ClassWithNullWrappedPrimitive();
     String json = gson.toJson(target);
     assertTrue(json.contains("\"value\":null"));
   }
-  
-  /** 
+
+  /**
    * Added to verify http://code.google.com/p/google-gson/issues/detail?id=68
    */
-  public void testNullWrappedPrimitiveMemberDeserialization() {
+  @Test
+  void testNullWrappedPrimitiveMemberDeserialization() {
     Gson gson = gsonBuilder.create();
     String json = "{'value':null}";
     ClassWithNullWrappedPrimitive target = gson.fromJson(json, ClassWithNullWrappedPrimitive.class);
     assertNull(target.value);
   }
-  
-  public void testExplicitSerializationOfNullCollectionMembers() {
+
+  @Test
+  void testExplicitSerializationOfNullCollectionMembers() {
     Gson gson = gsonBuilder.create();
     ClassWithMembers target = new ClassWithMembers();
     String json = gson.toJson(target);
     assertTrue(json.contains("\"col\":null"));
   }
-  
-  public void testExplicitSerializationOfNullStringMembers() {
+
+  @Test
+  void testExplicitSerializationOfNullStringMembers() {
     Gson gson = gsonBuilder.create();
     ClassWithMembers target = new ClassWithMembers();
     String json = gson.toJson(target);
     assertTrue(json.contains("\"str\":null"));
   }
 
-  public void testCustomSerializationOfNulls() {
+  @Test
+  void testCustomSerializationOfNulls() {
     gsonBuilder.registerTypeAdapter(ClassWithObjects.class, new ClassWithObjectsSerializer());
     Gson gson = gsonBuilder.create();
     ClassWithObjects target = new ClassWithObjects(new BagOfPrimitives());
@@ -126,8 +139,9 @@ public void testCustomSerializationOfNulls() {
     String expected = "{\"bag\":null}";
     assertEquals(expected, actual);
   }
-  
-  public void testPrintPrintingObjectWithNulls() throws Exception {
+
+  @Test
+  void testPrintPrintingObjectWithNulls() throws Exception {
     gsonBuilder = new GsonBuilder();
     Gson gson = gsonBuilder.create();
     String result = gson.toJson(new ClassWithMembers());
@@ -137,8 +151,9 @@ public void testPrintPrintingObjectWithNulls() throws Exception {
     result = gson.toJson(new ClassWithMembers());
     assertTrue(result.contains("\"str\":null"));
   }
-  
-  public void testPrintPrintingArraysWithNulls() throws Exception {
+
+  @Test
+  void testPrintPrintingArraysWithNulls() throws Exception {
     gsonBuilder = new GsonBuilder();
     Gson gson = gsonBuilder.create();
     String result = gson.toJson(new String[] { "1", null, "3" });
@@ -150,7 +165,8 @@ public void testPrintPrintingArraysWithNulls() throws Exception {
   }
 
   // test for issue 389
-  public void testAbsentJsonElementsAreSetToNull() {
+  @Test
+  void testAbsentJsonElementsAreSetToNull() {
     Gson gson = new Gson();
     ClassWithInitializedMembers target =
         gson.fromJson("{array:[1,2,3]}", ClassWithInitializedMembers.class);
@@ -163,7 +179,7 @@ public void testAbsentJsonElementsAreSetToNull() {
     assertFalse(target.bool2); // test the default value of a primitive boolean field per JVM spec
   }
 
-  public static class ClassWithInitializedMembers {
+  static class ClassWithInitializedMembers {
     // Using a mix of no-args constructor and field initializers
     // Also, some fields are intialized and some are not (so initialized per JVM spec)
     public static final String MY_STRING_DEFAULT = "string";
@@ -190,7 +206,7 @@ private static class ClassWithMembers {
     int[] array;
     Collection<String> col;
   }
-  
+
   private static class ClassWithObjectsSerializer implements JsonSerializer<ClassWithObjects> {
     @Override public JsonElement serialize(ClassWithObjects src, Type typeOfSrc,
         JsonSerializationContext context) {
@@ -200,14 +216,16 @@ private static class ClassWithObjectsSerializer implements JsonSerializer<ClassW
     }
   }
 
-  public void testExplicitNullSetsFieldToNullDuringDeserialization() {
+  @Test
+  void testExplicitNullSetsFieldToNullDuringDeserialization() {
     Gson gson = new Gson();
     String json = "{value:null}";
     ObjectWithField obj = gson.fromJson(json, ObjectWithField.class);
     assertNull(obj.value);
   }
 
-  public void testCustomTypeAdapterPassesNullSerialization() {
+  @Test
+  void testCustomTypeAdapterPassesNullSerialization() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(ObjectWithField.class, new JsonSerializer<ObjectWithField>() {
           @Override public JsonElement serialize(ObjectWithField src, Type typeOfSrc,
@@ -221,7 +239,8 @@ public void testCustomTypeAdapterPassesNullSerialization() {
     assertFalse(json.contains("value1"));
   }
 
-  public void testCustomTypeAdapterPassesNullDesrialization() {
+  @Test
+  void testCustomTypeAdapterPassesNullDesrialization() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(ObjectWithField.class, new JsonDeserializer<ObjectWithField>() {
           @Override public ObjectWithField deserialize(JsonElement json, Type type,
diff --git a/gson/src/test/java/com/google/gson/functional/ObjectTest.java b/gson/src/test/java/com/google/gson/functional/ObjectTest.java
index 48508f83b8..454062370a 100644
--- a/gson/src/test/java/com/google/gson/functional/ObjectTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ObjectTest.java
@@ -16,6 +16,13 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.InstanceCreator;
@@ -44,8 +51,9 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.TimeZone;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for Json serialization and deserialization of regular classes.
@@ -53,25 +61,29 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ObjectTest extends TestCase {
+class ObjectTest {
   private Gson gson;
-  private TimeZone oldTimeZone = TimeZone.getDefault();
+  private TimeZone oldTimeZone;
+  private Locale oldLocale;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
 
+    oldTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
+    oldLocale = Locale.getDefault();
     Locale.setDefault(Locale.US);
   }
 
-  @Override
-  protected void tearDown() throws Exception {
+  @AfterEach
+  void tearDown() throws Exception {
     TimeZone.setDefault(oldTimeZone);
-    super.tearDown();
+    Locale.setDefault(oldLocale);
   }
-  public void testJsonInSingleQuotesDeserialization() {
+
+  @Test
+  void testJsonInSingleQuotesDeserialization() {
     String json = "{'stringValue':'no message','intValue':10,'longValue':20}";
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals("no message", target.stringValue);
@@ -79,7 +91,8 @@ public void testJsonInSingleQuotesDeserialization() {
     assertEquals(20, target.longValue);
   }
 
-  public void testJsonInMixedQuotesDeserialization() {
+  @Test
+  void testJsonInMixedQuotesDeserialization() {
     String json = "{\"stringValue\":'no message','intValue':10,'longValue':20}";
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals("no message", target.stringValue);
@@ -87,84 +100,98 @@ public void testJsonInMixedQuotesDeserialization() {
     assertEquals(20, target.longValue);
   }
 
-  public void testBagOfPrimitivesSerialization() throws Exception {
+  @Test
+  void testBagOfPrimitivesSerialization() throws Exception {
     BagOfPrimitives target = new BagOfPrimitives(10, 20, false, "stringValue");
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testBagOfPrimitivesDeserialization() throws Exception {
+  @Test
+  void testBagOfPrimitivesDeserialization() throws Exception {
     BagOfPrimitives src = new BagOfPrimitives(10, 20, false, "stringValue");
     String json = src.getExpectedJson();
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(json, target.getExpectedJson());
   }
 
-  public void testBagOfPrimitiveWrappersSerialization() throws Exception {
+  @Test
+  void testBagOfPrimitiveWrappersSerialization() throws Exception {
     BagOfPrimitiveWrappers target = new BagOfPrimitiveWrappers(10L, 20, false);
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testBagOfPrimitiveWrappersDeserialization() throws Exception {
+  @Test
+  void testBagOfPrimitiveWrappersDeserialization() throws Exception {
     BagOfPrimitiveWrappers target = new BagOfPrimitiveWrappers(10L, 20, false);
     String jsonString = target.getExpectedJson();
     target = gson.fromJson(jsonString, BagOfPrimitiveWrappers.class);
     assertEquals(jsonString, target.getExpectedJson());
   }
 
-  public void testClassWithTransientFieldsSerialization() throws Exception {
+  @Test
+  void testClassWithTransientFieldsSerialization() throws Exception {
     ClassWithTransientFields<Long> target = new ClassWithTransientFields<Long>(1L);
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
   @SuppressWarnings("rawtypes")
-  public void testClassWithTransientFieldsDeserialization() throws Exception {
+  @Test
+  void testClassWithTransientFieldsDeserialization() throws Exception {
     String json = "{\"longValue\":[1]}";
     ClassWithTransientFields target = gson.fromJson(json, ClassWithTransientFields.class);
     assertEquals(json, target.getExpectedJson());
   }
 
   @SuppressWarnings("rawtypes")
-  public void testClassWithTransientFieldsDeserializationTransientFieldsPassedInJsonAreIgnored()
+  @Test
+  void testClassWithTransientFieldsDeserializationTransientFieldsPassedInJsonAreIgnored()
       throws Exception {
     String json = "{\"transientLongValue\":1,\"longValue\":[1]}";
     ClassWithTransientFields target = gson.fromJson(json, ClassWithTransientFields.class);
     assertFalse(target.transientLongValue != 1);
   }
 
-  public void testClassWithNoFieldsSerialization() throws Exception {
+  @Test
+  void testClassWithNoFieldsSerialization() throws Exception {
     assertEquals("{}", gson.toJson(new ClassWithNoFields()));
   }
 
-  public void testClassWithNoFieldsDeserialization() throws Exception {
+  @Test
+  void testClassWithNoFieldsDeserialization() throws Exception {
     String json = "{}";
     ClassWithNoFields target = gson.fromJson(json, ClassWithNoFields.class);
     ClassWithNoFields expected = new ClassWithNoFields();
     assertEquals(expected, target);
   }
 
-  public void testNestedSerialization() throws Exception {
+  @Test
+  void testNestedSerialization() throws Exception {
     Nested target = new Nested(new BagOfPrimitives(10, 20, false, "stringValue"),
        new BagOfPrimitives(30, 40, true, "stringValue"));
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testNestedDeserialization() throws Exception {
+  @Test
+  void testNestedDeserialization() throws Exception {
     String json = "{\"primitive1\":{\"longValue\":10,\"intValue\":20,\"booleanValue\":false,"
         + "\"stringValue\":\"stringValue\"},\"primitive2\":{\"longValue\":30,\"intValue\":40,"
         + "\"booleanValue\":true,\"stringValue\":\"stringValue\"}}";
     Nested target = gson.fromJson(json, Nested.class);
     assertEquals(json, target.getExpectedJson());
   }
-  public void testNullSerialization() throws Exception {
+  @Test
+  void testNullSerialization() throws Exception {
     assertEquals("null", gson.toJson(null));
   }
 
-  public void testEmptyStringDeserialization() throws Exception {
+  @Test
+  void testEmptyStringDeserialization() throws Exception {
     Object object = gson.fromJson("", Object.class);
     assertNull(object);
   }
 
-  public void testTruncatedDeserialization() {
+  @Test
+  void testTruncatedDeserialization() {
     try {
       gson.fromJson("[\"a\", \"b\",", new TypeToken<List<String>>() {}.getType());
       fail();
@@ -172,47 +199,55 @@ public void testTruncatedDeserialization() {
     }
   }
 
-  public void testNullDeserialization() throws Exception {
+  @Test
+  void testNullDeserialization() throws Exception {
     String myNullObject = null;
     Object object = gson.fromJson(myNullObject, Object.class);
     assertNull(object);
   }
 
-  public void testNullFieldsSerialization() throws Exception {
+  @Test
+  void testNullFieldsSerialization() throws Exception {
     Nested target = new Nested(new BagOfPrimitives(10, 20, false, "stringValue"), null);
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testNullFieldsDeserialization() throws Exception {
+  @Test
+  void testNullFieldsDeserialization() throws Exception {
     String json = "{\"primitive1\":{\"longValue\":10,\"intValue\":20,\"booleanValue\":false"
         + ",\"stringValue\":\"stringValue\"}}";
     Nested target = gson.fromJson(json, Nested.class);
     assertEquals(json, target.getExpectedJson());
   }
 
-  public void testArrayOfObjectsSerialization() throws Exception {
+  @Test
+  void testArrayOfObjectsSerialization() throws Exception {
     ArrayOfObjects target = new ArrayOfObjects();
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testArrayOfObjectsDeserialization() throws Exception {
+  @Test
+  void testArrayOfObjectsDeserialization() throws Exception {
     String json = new ArrayOfObjects().getExpectedJson();
     ArrayOfObjects target = gson.fromJson(json, ArrayOfObjects.class);
     assertEquals(json, target.getExpectedJson());
   }
 
-  public void testArrayOfArraysSerialization() throws Exception {
+  @Test
+  void testArrayOfArraysSerialization() throws Exception {
     ArrayOfArrays target = new ArrayOfArrays();
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testArrayOfArraysDeserialization() throws Exception {
+  @Test
+  void testArrayOfArraysDeserialization() throws Exception {
     String json = new ArrayOfArrays().getExpectedJson();
     ArrayOfArrays target = gson.fromJson(json, ArrayOfArrays.class);
     assertEquals(json, target.getExpectedJson());
   }
 
-  public void testArrayOfObjectsAsFields() throws Exception {
+  @Test
+  void testArrayOfObjectsAsFields() throws Exception {
     ClassWithObjects classWithObjects = new ClassWithObjects();
     BagOfPrimitives bagOfPrimitives = new BagOfPrimitives();
     String stringValue = "someStringValueInArray";
@@ -231,7 +266,8 @@ public void testArrayOfObjectsAsFields() throws Exception {
   /**
    * Created in response to Issue 14: http://code.google.com/p/google-gson/issues/detail?id=14
    */
-  public void testNullArraysDeserialization() throws Exception {
+  @Test
+  void testNullArraysDeserialization() throws Exception {
     String json = "{\"array\": null}";
     ClassWithArray target = gson.fromJson(json, ClassWithArray.class);
     assertNull(target.array);
@@ -240,13 +276,15 @@ public void testNullArraysDeserialization() throws Exception {
   /**
    * Created in response to Issue 14: http://code.google.com/p/google-gson/issues/detail?id=14
    */
-  public void testNullObjectFieldsDeserialization() throws Exception {
+  @Test
+  void testNullObjectFieldsDeserialization() throws Exception {
     String json = "{\"bag\": null}";
     ClassWithObjects target = gson.fromJson(json, ClassWithObjects.class);
     assertNull(target.bag);
   }
 
-  public void testEmptyCollectionInAnObjectDeserialization() throws Exception {
+  @Test
+  void testEmptyCollectionInAnObjectDeserialization() throws Exception {
     String json = "{\"children\":[]}";
     ClassWithCollectionField target = gson.fromJson(json, ClassWithCollectionField.class);
     assertNotNull(target);
@@ -257,7 +295,8 @@ private static class ClassWithCollectionField {
     Collection<String> children = new ArrayList<String>();
   }
 
-  public void testPrimitiveArrayInAnObjectDeserialization() throws Exception {
+  @Test
+  void testPrimitiveArrayInAnObjectDeserialization() throws Exception {
     String json = "{\"longArray\":[0,1,2,3,4,5,6,7,8,9]}";
     PrimitiveArray target = gson.fromJson(json, PrimitiveArray.class);
     assertEquals(json, target.getExpectedJson());
@@ -266,33 +305,39 @@ public void testPrimitiveArrayInAnObjectDeserialization() throws Exception {
   /**
    * Created in response to Issue 14: http://code.google.com/p/google-gson/issues/detail?id=14
    */
-  public void testNullPrimitiveFieldsDeserialization() throws Exception {
+  @Test
+  void testNullPrimitiveFieldsDeserialization() throws Exception {
     String json = "{\"longValue\":null}";
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(BagOfPrimitives.DEFAULT_VALUE, target.longValue);
   }
 
-  public void testEmptyCollectionInAnObjectSerialization() throws Exception {
+  @Test
+  void testEmptyCollectionInAnObjectSerialization() throws Exception {
     ClassWithCollectionField target = new ClassWithCollectionField();
     assertEquals("{\"children\":[]}", gson.toJson(target));
   }
 
-  public void testPrivateNoArgConstructorDeserialization() throws Exception {
+  @Test
+  void testPrivateNoArgConstructorDeserialization() throws Exception {
     ClassWithPrivateNoArgsConstructor target =
       gson.fromJson("{\"a\":20}", ClassWithPrivateNoArgsConstructor.class);
     assertEquals(20, target.a);
   }
 
-  public void testAnonymousLocalClassesSerialization() throws Exception {
+  @Test
+  void testAnonymousLocalClassesSerialization() throws Exception {
     assertEquals("null", gson.toJson(new ClassWithNoFields() {
       // empty anonymous class
     }));
   }
 
-  public void testAnonymousLocalClassesCustomSerialization() throws Exception {
+  @Test
+  void testAnonymousLocalClassesCustomSerialization() throws Exception {
     gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(ClassWithNoFields.class,
             new JsonSerializer<ClassWithNoFields>() {
+              @Override
               public JsonElement serialize(
                   ClassWithNoFields src, Type typeOfSrc, JsonSerializationContext context) {
                 return new JsonObject();
@@ -304,7 +349,8 @@ public JsonElement serialize(
     }));
   }
 
-  public void testPrimitiveArrayFieldSerialization() {
+  @Test
+  void testPrimitiveArrayFieldSerialization() {
     PrimitiveArray target = new PrimitiveArray(new long[] { 1L, 2L, 3L });
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
@@ -313,7 +359,8 @@ public void testPrimitiveArrayFieldSerialization() {
    * Tests that a class field with type Object can be serialized properly.
    * See issue 54
    */
-  public void testClassWithObjectFieldSerialization() {
+  @Test
+  void testClassWithObjectFieldSerialization() {
     ClassWithObjectField obj = new ClassWithObjectField();
     obj.member = "abc";
     String json = gson.toJson(obj);
@@ -325,7 +372,8 @@ private static class ClassWithObjectField {
     Object member;
   }
 
-  public void testInnerClassSerialization() {
+  @Test
+  void testInnerClassSerialization() {
     Parent p = new Parent();
     Parent.Child c = p.new Child();
     String json = gson.toJson(c);
@@ -333,10 +381,12 @@ public void testInnerClassSerialization() {
     assertFalse(json.contains("value1"));
   }
 
-  public void testInnerClassDeserialization() {
+  @Test
+  void testInnerClassDeserialization() {
     final Parent p = new Parent();
     Gson gson = new GsonBuilder().registerTypeAdapter(
         Parent.Child.class, new InstanceCreator<Parent.Child>() {
+      @Override
       public Parent.Child createInstance(Type type) {
         return p.new Child();
       }
@@ -401,7 +451,8 @@ private ClassWithPrivateNoArgsConstructor() {
   /**
    * In response to Issue 41 http://code.google.com/p/google-gson/issues/detail?id=41
    */
-  public void testObjectFieldNamesWithoutQuotesDeserialization() {
+  @Test
+  void testObjectFieldNamesWithoutQuotesDeserialization() {
     String json = "{longValue:1,'booleanValue':true,\"stringValue\":'bar'}";
     BagOfPrimitives bag = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(1, bag.longValue);
@@ -409,7 +460,8 @@ public void testObjectFieldNamesWithoutQuotesDeserialization() {
     assertEquals("bar", bag.stringValue);
   }
 
-  public void testStringFieldWithNumberValueDeserialization() {
+  @Test
+  void testStringFieldWithNumberValueDeserialization() {
     String json = "{\"stringValue\":1}";
     BagOfPrimitives bag = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals("1", bag.stringValue);
@@ -426,7 +478,8 @@ public void testStringFieldWithNumberValueDeserialization() {
   /**
    * Created to reproduce issue 140
    */
-  public void testStringFieldWithEmptyValueSerialization() {
+  @Test
+  void testStringFieldWithEmptyValueSerialization() {
     ClassWithEmptyStringFields target = new ClassWithEmptyStringFields();
     target.a = "5794749";
     String json = gson.toJson(target);
@@ -438,7 +491,8 @@ public void testStringFieldWithEmptyValueSerialization() {
   /**
    * Created to reproduce issue 140
    */
-  public void testStringFieldWithEmptyValueDeserialization() {
+  @Test
+  void testStringFieldWithEmptyValueDeserialization() {
     String json = "{a:\"5794749\",b:\"\",c:\"\"}";
     ClassWithEmptyStringFields target = gson.fromJson(json, ClassWithEmptyStringFields.class);
     assertEquals("5794749", target.a);
@@ -452,7 +506,8 @@ private static class ClassWithEmptyStringFields {
     String c = "";
   }
 
-  public void testJsonObjectSerialization() {
+  @Test
+  void testJsonObjectSerialization() {
     Gson gson = new GsonBuilder().serializeNulls().create();
     JsonObject obj = new JsonObject();
     String json = gson.toJson(obj);
@@ -462,7 +517,8 @@ public void testJsonObjectSerialization() {
   /**
    * Test for issue 215.
    */
-  public void testSingletonLists() {
+  @Test
+  void testSingletonLists() {
     Gson gson = new Gson();
     Product product = new Product();
     assertEquals("{\"attributes\":[],\"departments\":[]}",
@@ -481,7 +537,8 @@ public void testSingletonLists() {
   }
 
   // http://code.google.com/p/google-gson/issues/detail?id=270
-  public void testDateAsMapObjectField() {
+  @Test
+  void testDateAsMapObjectField() {
     HasObjectMap a = new HasObjectMap();
     a.map.put("date", new Date(0));
     if (JavaVersion.isJava9OrLater()) {
@@ -491,7 +548,7 @@ public void testDateAsMapObjectField() {
     }
   }
 
-  public class HasObjectMap {
+  class HasObjectMap {
     Map<String, Object> map = new HashMap<String, Object>();
   }
 
diff --git a/gson/src/test/java/com/google/gson/functional/ParameterizedTypesTest.java b/gson/src/test/java/com/google/gson/functional/ParameterizedTypesTest.java
index ef805655fc..c27b8c9633 100644
--- a/gson/src/test/java/com/google/gson/functional/ParameterizedTypesTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ParameterizedTypesTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.ParameterizedTypeFixtures.MyParameterizedType;
@@ -23,9 +26,6 @@
 import com.google.gson.ParameterizedTypeFixtures.MyParameterizedTypeInstanceCreator;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.io.Reader;
 import java.io.Serializable;
 import java.io.StringReader;
@@ -35,6 +35,8 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the serialization and deserialization of parameterized types in Gson.
@@ -42,23 +44,24 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ParameterizedTypesTest extends TestCase {
+class ParameterizedTypesTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testParameterizedTypesSerialization() throws Exception {
+  @Test
+  void testParameterizedTypesSerialization() throws Exception {
     MyParameterizedType<Integer> src = new MyParameterizedType<Integer>(10);
     Type typeOfSrc = new TypeToken<MyParameterizedType<Integer>>() {}.getType();
     String json = gson.toJson(src, typeOfSrc);
     assertEquals(src.getExpectedJson(), json);
   }
 
-  public void testParameterizedTypeDeserialization() throws Exception {
+  @Test
+  void testParameterizedTypeDeserialization() throws Exception {
     BagOfPrimitives bag = new BagOfPrimitives();
     MyParameterizedType<BagOfPrimitives> expected = new MyParameterizedType<BagOfPrimitives>(bag);
     Type expectedType = new TypeToken<MyParameterizedType<BagOfPrimitives>>() {}.getType();
@@ -72,7 +75,8 @@ public void testParameterizedTypeDeserialization() throws Exception {
     assertEquals(expected, actual);
   }
 
-  public void testTypesWithMultipleParametersSerialization() throws Exception {
+  @Test
+  void testTypesWithMultipleParametersSerialization() throws Exception {
     MultiParameters<Integer, Float, Double, String, BagOfPrimitives> src =
         new MultiParameters<Integer, Float, Double, String, BagOfPrimitives>(10, 1.0F, 2.1D,
             "abc", new BagOfPrimitives());
@@ -84,7 +88,8 @@ public void testTypesWithMultipleParametersSerialization() throws Exception {
     assertEquals(expected, json);
   }
 
-  public void testTypesWithMultipleParametersDeserialization() throws Exception {
+  @Test
+  void testTypesWithMultipleParametersDeserialization() throws Exception {
     Type typeOfTarget = new TypeToken<MultiParameters<Integer, Float, Double, String,
         BagOfPrimitives>>() {}.getType();
     String json = "{\"a\":10,\"b\":1.0,\"c\":2.1,\"d\":\"abc\","
@@ -97,7 +102,8 @@ public void testTypesWithMultipleParametersDeserialization() throws Exception {
     assertEquals(expected, target);
   }
 
-  public void testParameterizedTypeWithCustomSerializer() {
+  @Test
+  void testParameterizedTypeWithCustomSerializer() {
     Type ptIntegerType = new TypeToken<MyParameterizedType<Integer>>() {}.getType();
     Type ptStringType = new TypeToken<MyParameterizedType<String>>() {}.getType();
     Gson gson = new GsonBuilder()
@@ -113,7 +119,8 @@ public void testParameterizedTypeWithCustomSerializer() {
     assertEquals(MyParameterizedTypeAdapter.<String>getExpectedJson(stringTarget), json);
   }
 
-  public void testParameterizedTypesWithCustomDeserializer() {
+  @Test
+  void testParameterizedTypesWithCustomDeserializer() {
     Type ptIntegerType = new TypeToken<MyParameterizedType<Integer>>() {}.getType();
     Type ptStringType = new TypeToken<MyParameterizedType<String>>() {}.getType();
     Gson gson = new GsonBuilder().registerTypeAdapter(
@@ -135,7 +142,8 @@ public void testParameterizedTypesWithCustomDeserializer() {
     assertEquals("abc", stringTarget.value);
   }
 
-  public void testParameterizedTypesWithWriterSerialization() throws Exception {
+  @Test
+  void testParameterizedTypesWithWriterSerialization() throws Exception {
     Writer writer = new StringWriter();
     MyParameterizedType<Integer> src = new MyParameterizedType<Integer>(10);
     Type typeOfSrc = new TypeToken<MyParameterizedType<Integer>>() {}.getType();
@@ -143,7 +151,8 @@ public void testParameterizedTypesWithWriterSerialization() throws Exception {
     assertEquals(src.getExpectedJson(), writer.toString());
   }
 
-  public void testParameterizedTypeWithReaderDeserialization() throws Exception {
+  @Test
+  void testParameterizedTypeWithReaderDeserialization() throws Exception {
     BagOfPrimitives bag = new BagOfPrimitives();
     MyParameterizedType<BagOfPrimitives> expected = new MyParameterizedType<BagOfPrimitives>(bag);
     Type expectedType = new TypeToken<MyParameterizedType<BagOfPrimitives>>() {}.getType();
@@ -158,7 +167,8 @@ public void testParameterizedTypeWithReaderDeserialization() throws Exception {
   }
 
   @SuppressWarnings("unchecked")
-  public void testVariableTypeFieldsAndGenericArraysSerialization() throws Exception {
+  @Test
+  void testVariableTypeFieldsAndGenericArraysSerialization() throws Exception {
     Integer obj = 0;
     Integer[] array = { 1, 2, 3 };
     List<Integer> list = new ArrayList<Integer>();
@@ -175,7 +185,8 @@ public void testVariableTypeFieldsAndGenericArraysSerialization() throws Excepti
   }
 
   @SuppressWarnings("unchecked")
-  public void testVariableTypeFieldsAndGenericArraysDeserialization() throws Exception {
+  @Test
+  void testVariableTypeFieldsAndGenericArraysDeserialization() throws Exception {
     Integer obj = 0;
     Integer[] array = { 1, 2, 3 };
     List<Integer> list = new ArrayList<Integer>();
@@ -192,7 +203,8 @@ public void testVariableTypeFieldsAndGenericArraysDeserialization() throws Excep
     assertEquals(objAfterDeserialization.getExpectedJson(), json);
   }
 
-  public void testVariableTypeDeserialization() throws Exception {
+  @Test
+  void testVariableTypeDeserialization() throws Exception {
     Type typeOfSrc = new TypeToken<ObjectWithTypeVariables<Integer>>() {}.getType();
     ObjectWithTypeVariables<Integer> objToSerialize =
         new ObjectWithTypeVariables<Integer>(0, null, null, null, null, null);
@@ -202,7 +214,8 @@ public void testVariableTypeDeserialization() throws Exception {
     assertEquals(objAfterDeserialization.getExpectedJson(), json);
   }
 
-  public void testVariableTypeArrayDeserialization() throws Exception {
+  @Test
+  void testVariableTypeArrayDeserialization() throws Exception {
     Integer[] array = { 1, 2, 3 };
 
     Type typeOfSrc = new TypeToken<ObjectWithTypeVariables<Integer>>() {}.getType();
@@ -214,7 +227,8 @@ public void testVariableTypeArrayDeserialization() throws Exception {
     assertEquals(objAfterDeserialization.getExpectedJson(), json);
   }
 
-  public void testParameterizedTypeWithVariableTypeDeserialization() throws Exception {
+  @Test
+  void testParameterizedTypeWithVariableTypeDeserialization() throws Exception {
     List<Integer> list = new ArrayList<Integer>();
     list.add(4);
     list.add(5);
@@ -229,7 +243,8 @@ public void testParameterizedTypeWithVariableTypeDeserialization() throws Except
   }
 
   @SuppressWarnings("unchecked")
-  public void testParameterizedTypeGenericArraysSerialization() throws Exception {
+  @Test
+  void testParameterizedTypeGenericArraysSerialization() throws Exception {
     List<Integer> list = new ArrayList<Integer>();
     list.add(1);
     list.add(2);
@@ -243,7 +258,8 @@ public void testParameterizedTypeGenericArraysSerialization() throws Exception {
   }
 
   @SuppressWarnings("unchecked")
-  public void testParameterizedTypeGenericArraysDeserialization() throws Exception {
+  @Test
+  void testParameterizedTypeGenericArraysDeserialization() throws Exception {
     List<Integer> list = new ArrayList<Integer>();
     list.add(1);
     list.add(2);
@@ -462,7 +478,7 @@ public boolean equals(Object obj) {
       return true;
     }
   }
-  
+
   // Begin: tests to reproduce issue 103
   private static class Quantity {
     @SuppressWarnings("unused")
@@ -478,22 +494,24 @@ private interface Field<T> {
   }
   private interface Immutable {
   }
-  
-  public static final class Amount<Q extends Quantity> 
+
+  static final class Amount<Q extends Quantity>
       implements Measurable<Q>, Field<Amount<?>>, Serializable, Immutable {
     private static final long serialVersionUID = -7560491093120970437L;
 
     int value = 30;
   }
-  
-  public void testDeepParameterizedTypeSerialization() {
+
+  @Test
+  void testDeepParameterizedTypeSerialization() {
     Amount<MyQuantity> amount = new Amount<MyQuantity>();
     String json = gson.toJson(amount);
     assertTrue(json.contains("value"));
     assertTrue(json.contains("30"));
   }
-  
-  public void testDeepParameterizedTypeDeserialization() {
+
+  @Test
+  void testDeepParameterizedTypeDeserialization() {
     String json = "{value:30}";
     Type type = new TypeToken<Amount<MyQuantity>>() {}.getType();
     Amount<MyQuantity> amount = gson.fromJson(json, type);
diff --git a/gson/src/test/java/com/google/gson/functional/PrettyPrintingTest.java b/gson/src/test/java/com/google/gson/functional/PrettyPrintingTest.java
index 0aacc9e27a..704e056375 100644
--- a/gson/src/test/java/com/google/gson/functional/PrettyPrintingTest.java
+++ b/gson/src/test/java/com/google/gson/functional/PrettyPrintingTest.java
@@ -15,20 +15,22 @@
  */
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
-import java.util.Arrays;
-import java.util.LinkedHashMap;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Map;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.common.TestTypes.ArrayOfObjects;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.reflect.TypeToken;
+import java.lang.reflect.Type;
+import java.util.Arrays;
+import java.util.LinkedHashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for pretty printing option.
@@ -36,19 +38,19 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class PrettyPrintingTest extends TestCase {
+class PrettyPrintingTest {
 
   private static final boolean DEBUG = false;
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder().setPrettyPrinting().create();
   }
 
-  public void testPrettyPrintList() {
+  @Test
+  void testPrettyPrintList() {
     BagOfPrimitives b = new BagOfPrimitives();
     List<BagOfPrimitives> listOfB = new LinkedList<BagOfPrimitives>();
     for (int i = 0; i < 15; ++i) {
@@ -59,19 +61,22 @@ public void testPrettyPrintList() {
     print(json);
   }
 
-  public void testPrettyPrintArrayOfObjects() {
+  @Test
+  void testPrettyPrintArrayOfObjects() {
     ArrayOfObjects target = new ArrayOfObjects();
     String json = gson.toJson(target);
     print(json);
   }
 
-  public void testPrettyPrintArrayOfPrimitives() {
+  @Test
+  void testPrettyPrintArrayOfPrimitives() {
     int[] ints = new int[] { 1, 2, 3, 4, 5 };
     String json = gson.toJson(ints);
     assertEquals("[\n  1,\n  2,\n  3,\n  4,\n  5\n]", json);
   }
 
-  public void testPrettyPrintArrayOfPrimitiveArrays() {
+  @Test
+  void testPrettyPrintArrayOfPrimitiveArrays() {
     int[][] ints = new int[][] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 },
         { 9, 0 }, { 10 } };
     String json = gson.toJson(ints);
@@ -79,15 +84,17 @@ public void testPrettyPrintArrayOfPrimitiveArrays() {
         + "\n  [\n    7,\n    8\n  ],\n  [\n    9,\n    0\n  ],\n  [\n    10\n  ]\n]", json);
   }
 
-  public void testPrettyPrintListOfPrimitiveArrays() {
+  @Test
+  void testPrettyPrintListOfPrimitiveArrays() {
     List<Integer[]> list = Arrays.asList(new Integer[][] { { 1, 2 }, { 3, 4 },
         { 5, 6 }, { 7, 8 }, { 9, 0 }, { 10 } });
     String json = gson.toJson(list);
     assertEquals("[\n  [\n    1,\n    2\n  ],\n  [\n    3,\n    4\n  ],\n  [\n    5,\n    6\n  ],"
         + "\n  [\n    7,\n    8\n  ],\n  [\n    9,\n    0\n  ],\n  [\n    10\n  ]\n]", json);
   }
-  
-  public void testMap() {
+
+  @Test
+  void testMap() {
     Map<String, Integer> map = new LinkedHashMap<String, Integer>();
     map.put("abc", 1);
     map.put("def", 5);
@@ -96,7 +103,8 @@ public void testMap() {
   }
 
   // In response to bug 153
-  public void testEmptyMapField() {
+  @Test
+  void testEmptyMapField() {
     ClassWithMap obj = new ClassWithMap();
     obj.map = new LinkedHashMap<String, Integer>();
     String json = gson.toJson(obj);
@@ -109,7 +117,8 @@ private static class ClassWithMap {
     int value = 2;
   }
 
-  public void testMultipleArrays() {
+  @Test
+  void testMultipleArrays() {
     int[][][] ints = new int[][][] { { { 1 }, { 2 } } };
     String json = gson.toJson(ints);
     assertEquals("[\n  [\n    [\n      1\n    ],\n    [\n      2\n    ]\n  ]\n]", json);
diff --git a/gson/src/test/java/com/google/gson/functional/PrimitiveCharacterTest.java b/gson/src/test/java/com/google/gson/functional/PrimitiveCharacterTest.java
index 69ff1f3f2a..ed59b4aefb 100644
--- a/gson/src/test/java/com/google/gson/functional/PrimitiveCharacterTest.java
+++ b/gson/src/test/java/com/google/gson/functional/PrimitiveCharacterTest.java
@@ -16,9 +16,11 @@
 
 package com.google.gson.functional;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.Gson;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for Java Character values.
@@ -26,22 +28,23 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class PrimitiveCharacterTest extends TestCase {
+class PrimitiveCharacterTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testPrimitiveCharacterAutoboxedSerialization() {
+  @Test
+  void testPrimitiveCharacterAutoboxedSerialization() {
     assertEquals("\"A\"", gson.toJson('A'));
     assertEquals("\"A\"", gson.toJson('A', char.class));
     assertEquals("\"A\"", gson.toJson('A', Character.class));
   }
 
-  public void testPrimitiveCharacterAutoboxedDeserialization() {
+  @Test
+  void testPrimitiveCharacterAutoboxedDeserialization() {
     char expected = 'a';
     char actual = gson.fromJson("a", char.class);
     assertEquals(expected, actual);
diff --git a/gson/src/test/java/com/google/gson/functional/PrimitiveTest.java b/gson/src/test/java/com/google/gson/functional/PrimitiveTest.java
index 55e612fa46..f8a9041db6 100644
--- a/gson/src/test/java/com/google/gson/functional/PrimitiveTest.java
+++ b/gson/src/test/java/com/google/gson/functional/PrimitiveTest.java
@@ -16,7 +16,11 @@
 
 package com.google.gson.functional;
 
-import static org.junit.Assert.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -30,7 +34,8 @@
 import java.math.BigInteger;
 import java.util.Arrays;
 import java.util.List;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for Json primitive values: integers, and floating point numbers.
@@ -38,20 +43,21 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class PrimitiveTest extends TestCase {
+class PrimitiveTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testPrimitiveIntegerAutoboxedSerialization() {
+  @Test
+  void testPrimitiveIntegerAutoboxedSerialization() {
     assertEquals("1", gson.toJson(1));
   }
 
-  public void testPrimitiveIntegerAutoboxedDeserialization() {
+  @Test
+  void testPrimitiveIntegerAutoboxedDeserialization() {
     int expected = 1;
     int actual = gson.fromJson("1", int.class);
     assertEquals(expected, actual);
@@ -60,12 +66,14 @@ public void testPrimitiveIntegerAutoboxedDeserialization() {
     assertEquals(expected, actual);
   }
 
-  public void testByteSerialization() {
+  @Test
+  void testByteSerialization() {
     assertEquals("1", gson.toJson(1, byte.class));
     assertEquals("1", gson.toJson(1, Byte.class));
   }
 
-  public void testByteDeserialization() {
+  @Test
+  void testByteDeserialization() {
     Byte boxed = gson.fromJson("1", Byte.class);
     assertEquals(1, (byte)boxed);
     byte primitive = gson.fromJson("1", byte.class);
@@ -75,7 +83,8 @@ public void testByteDeserialization() {
     assertArrayEquals(new byte[] {-128, 0, 127, -1}, bytes);
   }
 
-  public void testByteDeserializationLossy() {
+  @Test
+  void testByteDeserializationLossy() {
     try {
       gson.fromJson("-129", byte.class);
       fail();
@@ -98,12 +107,14 @@ public void testByteDeserializationLossy() {
     }
   }
 
-  public void testShortSerialization() {
+  @Test
+  void testShortSerialization() {
     assertEquals("1", gson.toJson(1, short.class));
     assertEquals("1", gson.toJson(1, Short.class));
   }
 
-  public void testShortDeserialization() {
+  @Test
+  void testShortDeserialization() {
     Short boxed = gson.fromJson("1", Short.class);
     assertEquals(1, (short)boxed);
     short primitive = gson.fromJson("1", short.class);
@@ -113,7 +124,8 @@ public void testShortDeserialization() {
     assertArrayEquals(new short[] {-32768, 0, 32767, -1}, shorts);
   }
 
-  public void testShortDeserializationLossy() {
+  @Test
+  void testShortDeserializationLossy() {
     try {
       gson.fromJson("-32769", short.class);
       fail();
@@ -136,30 +148,35 @@ public void testShortDeserializationLossy() {
     }
   }
 
-  public void testPrimitiveIntegerAutoboxedInASingleElementArraySerialization() {
+  @Test
+  void testPrimitiveIntegerAutoboxedInASingleElementArraySerialization() {
     int target[] = {-9332};
     assertEquals("[-9332]", gson.toJson(target));
     assertEquals("[-9332]", gson.toJson(target, int[].class));
     assertEquals("[-9332]", gson.toJson(target, Integer[].class));
   }
 
-  public void testReallyLongValuesSerialization() {
+  @Test
+  void testReallyLongValuesSerialization() {
     long value = 333961828784581L;
     assertEquals("333961828784581", gson.toJson(value));
   }
 
-  public void testReallyLongValuesDeserialization() {
+  @Test
+  void testReallyLongValuesDeserialization() {
     String json = "333961828784581";
     long value = gson.fromJson(json, Long.class);
     assertEquals(333961828784581L, value);
   }
 
-  public void testPrimitiveLongAutoboxedSerialization() {
+  @Test
+  void testPrimitiveLongAutoboxedSerialization() {
     assertEquals("1", gson.toJson(1L, long.class));
     assertEquals("1", gson.toJson(1L, Long.class));
   }
 
-  public void testPrimitiveLongAutoboxedDeserialization() {
+  @Test
+  void testPrimitiveLongAutoboxedDeserialization() {
     long expected = 1L;
     long actual = gson.fromJson("1", long.class);
     assertEquals(expected, actual);
@@ -168,33 +185,38 @@ public void testPrimitiveLongAutoboxedDeserialization() {
     assertEquals(expected, actual);
   }
 
-  public void testPrimitiveLongAutoboxedInASingleElementArraySerialization() {
+  @Test
+  void testPrimitiveLongAutoboxedInASingleElementArraySerialization() {
     long[] target = {-23L};
     assertEquals("[-23]", gson.toJson(target));
     assertEquals("[-23]", gson.toJson(target, long[].class));
     assertEquals("[-23]", gson.toJson(target, Long[].class));
   }
 
-  public void testPrimitiveBooleanAutoboxedSerialization() {
+  @Test
+  void testPrimitiveBooleanAutoboxedSerialization() {
     assertEquals("true", gson.toJson(true));
     assertEquals("false", gson.toJson(false));
   }
 
-  public void testBooleanDeserialization() {
+  @Test
+  void testBooleanDeserialization() {
     boolean value = gson.fromJson("false", boolean.class);
     assertEquals(false, value);
     value = gson.fromJson("true", boolean.class);
     assertEquals(true, value);
   }
 
-  public void testPrimitiveBooleanAutoboxedInASingleElementArraySerialization() {
+  @Test
+  void testPrimitiveBooleanAutoboxedInASingleElementArraySerialization() {
     boolean target[] = {false};
     assertEquals("[false]", gson.toJson(target));
     assertEquals("[false]", gson.toJson(target, boolean[].class));
     assertEquals("[false]", gson.toJson(target, Boolean[].class));
   }
 
-  public void testNumberSerialization() {
+  @Test
+  void testNumberSerialization() {
     Number expected = 1L;
     String json = gson.toJson(expected);
     assertEquals(expected.toString(), json);
@@ -203,7 +225,8 @@ public void testNumberSerialization() {
     assertEquals(expected.toString(), json);
   }
 
-  public void testNumberDeserialization() {
+  @Test
+  void testNumberDeserialization() {
     String json = "1";
     Number expected = Integer.valueOf(json);
     Number actual = gson.fromJson(json, Number.class);
@@ -219,17 +242,20 @@ public void testNumberDeserialization() {
     assertEquals(1L, actual.longValue());
   }
 
-  public void testNumberAsStringDeserialization() {
+  @Test
+  void testNumberAsStringDeserialization() {
     Number value = gson.fromJson("\"18\"", Number.class);
     assertEquals(18, value.intValue());
   }
 
-  public void testPrimitiveDoubleAutoboxedSerialization() {
+  @Test
+  void testPrimitiveDoubleAutoboxedSerialization() {
     assertEquals("-122.08234335", gson.toJson(-122.08234335D));
     assertEquals("122.08112002", gson.toJson(122.08112002D));
   }
 
-  public void testPrimitiveDoubleAutoboxedDeserialization() {
+  @Test
+  void testPrimitiveDoubleAutoboxedDeserialization() {
     double actual = gson.fromJson("-122.08858585", double.class);
     assertEquals(-122.08858585D, actual);
 
@@ -237,14 +263,16 @@ public void testPrimitiveDoubleAutoboxedDeserialization() {
     assertEquals(122.023900008D, actual);
   }
 
-  public void testPrimitiveDoubleAutoboxedInASingleElementArraySerialization() {
+  @Test
+  void testPrimitiveDoubleAutoboxedInASingleElementArraySerialization() {
     double[] target = {-122.08D};
     assertEquals("[-122.08]", gson.toJson(target));
     assertEquals("[-122.08]", gson.toJson(target, double[].class));
     assertEquals("[-122.08]", gson.toJson(target, Double[].class));
   }
 
-  public void testDoubleAsStringRepresentationDeserialization() {
+  @Test
+  void testDoubleAsStringRepresentationDeserialization() {
     String doubleValue = "1.0043E+5";
     Double expected = Double.valueOf(doubleValue);
     Double actual = gson.fromJson(doubleValue, Double.class);
@@ -254,7 +282,8 @@ public void testDoubleAsStringRepresentationDeserialization() {
     assertEquals(expected.doubleValue(), actual1);
   }
 
-  public void testDoubleNoFractAsStringRepresentationDeserialization() {
+  @Test
+  void testDoubleNoFractAsStringRepresentationDeserialization() {
     String doubleValue = "1E+5";
     Double expected = Double.valueOf(doubleValue);
     Double actual = gson.fromJson(doubleValue, Double.class);
@@ -264,7 +293,8 @@ public void testDoubleNoFractAsStringRepresentationDeserialization() {
     assertEquals(expected.doubleValue(), actual1);
   }
 
-  public void testDoubleArrayDeserialization() {
+  @Test
+  void testDoubleArrayDeserialization() {
       String json = "[0.0, 0.004761904761904762, 3.4013606962703525E-4, 7.936508173034305E-4,"
               + "0.0011904761904761906, 0.0]";
       double[] values = gson.fromJson(json, double[].class);
@@ -277,7 +307,8 @@ public void testDoubleArrayDeserialization() {
       assertEquals(0.0, values[5]);
   }
 
-  public void testLargeDoubleDeserialization() {
+  @Test
+  void testLargeDoubleDeserialization() {
     String doubleValue = "1.234567899E8";
     Double expected = Double.valueOf(doubleValue);
     Double actual = gson.fromJson(doubleValue, Double.class);
@@ -287,19 +318,22 @@ public void testLargeDoubleDeserialization() {
     assertEquals(expected.doubleValue(), actual1);
   }
 
-  public void testBigDecimalSerialization() {
+  @Test
+  void testBigDecimalSerialization() {
     BigDecimal target = new BigDecimal("-122.0e-21");
     String json = gson.toJson(target);
     assertEquals(target, new BigDecimal(json));
   }
 
-  public void testBigDecimalDeserialization() {
+  @Test
+  void testBigDecimalDeserialization() {
     BigDecimal target = new BigDecimal("-122.0e-21");
     String json = "-122.0e-21";
     assertEquals(target, gson.fromJson(json, BigDecimal.class));
   }
 
-  public void testBigDecimalInASingleElementArraySerialization() {
+  @Test
+  void testBigDecimalInASingleElementArraySerialization() {
     BigDecimal[] target = {new BigDecimal("-122.08e-21")};
     String json = gson.toJson(target);
     String actual = extractElementFromArray(json);
@@ -310,19 +344,22 @@ public void testBigDecimalInASingleElementArraySerialization() {
     assertEquals(target[0], new BigDecimal(actual));
   }
 
-  public void testSmallValueForBigDecimalSerialization() {
+  @Test
+  void testSmallValueForBigDecimalSerialization() {
     BigDecimal target = new BigDecimal("1.55");
     String actual = gson.toJson(target);
     assertEquals(target.toString(), actual);
   }
 
-  public void testSmallValueForBigDecimalDeserialization() {
+  @Test
+  void testSmallValueForBigDecimalDeserialization() {
     BigDecimal expected = new BigDecimal("1.55");
     BigDecimal actual = gson.fromJson("1.55", BigDecimal.class);
     assertEquals(expected, actual);
   }
 
-  public void testBigDecimalPreservePrecisionSerialization() {
+  @Test
+  void testBigDecimalPreservePrecisionSerialization() {
     String expectedValue = "1.000";
     BigDecimal obj = new BigDecimal(expectedValue);
     String actualValue = gson.toJson(obj);
@@ -330,7 +367,8 @@ public void testBigDecimalPreservePrecisionSerialization() {
     assertEquals(expectedValue, actualValue);
   }
 
-  public void testBigDecimalPreservePrecisionDeserialization() {
+  @Test
+  void testBigDecimalPreservePrecisionDeserialization() {
     String json = "1.000";
     BigDecimal expected = new BigDecimal(json);
     BigDecimal actual = gson.fromJson(json, BigDecimal.class);
@@ -338,32 +376,37 @@ public void testBigDecimalPreservePrecisionDeserialization() {
     assertEquals(expected, actual);
   }
 
-  public void testBigDecimalAsStringRepresentationDeserialization() {
+  @Test
+  void testBigDecimalAsStringRepresentationDeserialization() {
     String doubleValue = "0.05E+5";
     BigDecimal expected = new BigDecimal(doubleValue);
     BigDecimal actual = gson.fromJson(doubleValue, BigDecimal.class);
     assertEquals(expected, actual);
   }
 
-  public void testBigDecimalNoFractAsStringRepresentationDeserialization() {
+  @Test
+  void testBigDecimalNoFractAsStringRepresentationDeserialization() {
     String doubleValue = "5E+5";
     BigDecimal expected = new BigDecimal(doubleValue);
     BigDecimal actual = gson.fromJson(doubleValue, BigDecimal.class);
     assertEquals(expected, actual);
   }
 
-  public void testBigIntegerSerialization() {
+  @Test
+  void testBigIntegerSerialization() {
     BigInteger target = new BigInteger("12121211243123245845384534687435634558945453489543985435");
     assertEquals(target.toString(), gson.toJson(target));
   }
 
-  public void testBigIntegerDeserialization() {
+  @Test
+  void testBigIntegerDeserialization() {
     String json = "12121211243123245845384534687435634558945453489543985435";
     BigInteger target = new BigInteger(json);
     assertEquals(target, gson.fromJson(json, BigInteger.class));
   }
 
-  public void testBigIntegerInASingleElementArraySerialization() {
+  @Test
+  void testBigIntegerInASingleElementArraySerialization() {
     BigInteger[] target = {new BigInteger("1212121243434324323254365345367456456456465464564564")};
     String json = gson.toJson(target);
     String actual = extractElementFromArray(json);
@@ -374,26 +417,30 @@ public void testBigIntegerInASingleElementArraySerialization() {
     assertEquals(target[0], new BigInteger(actual));
   }
 
-  public void testSmallValueForBigIntegerSerialization() {
+  @Test
+  void testSmallValueForBigIntegerSerialization() {
     BigInteger target = new BigInteger("15");
     String actual = gson.toJson(target);
     assertEquals(target.toString(), actual);
   }
 
-  public void testSmallValueForBigIntegerDeserialization() {
+  @Test
+  void testSmallValueForBigIntegerDeserialization() {
     BigInteger expected = new BigInteger("15");
     BigInteger actual = gson.fromJson("15", BigInteger.class);
     assertEquals(expected, actual);
   }
 
-  public void testBadValueForBigIntegerDeserialization() {
+  @Test
+  void testBadValueForBigIntegerDeserialization() {
     try {
       gson.fromJson("15.099", BigInteger.class);
       fail("BigInteger can not be decimal values.");
     } catch (JsonSyntaxException expected) { }
   }
 
-  public void testMoreSpecificSerialization() {
+  @Test
+  void testMoreSpecificSerialization() {
     Gson gson = new Gson();
     String expected = "This is a string";
     String expectedJson = gson.toJson(expected);
@@ -407,7 +454,8 @@ private String extractElementFromArray(String json) {
     return json.substring(json.indexOf('[') + 1, json.indexOf(']'));
   }
 
-  public void testDoubleNaNSerializationNotSupportedByDefault() {
+  @Test
+  void testDoubleNaNSerializationNotSupportedByDefault() {
     try {
       double nan = Double.NaN;
       gson.toJson(nan);
@@ -421,19 +469,22 @@ public void testDoubleNaNSerializationNotSupportedByDefault() {
     }
   }
 
-  public void testDoubleNaNSerialization() {
+  @Test
+  void testDoubleNaNSerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     double nan = Double.NaN;
     assertEquals("NaN", gson.toJson(nan));
     assertEquals("NaN", gson.toJson(Double.NaN));
   }
 
-  public void testDoubleNaNDeserialization() {
+  @Test
+  void testDoubleNaNDeserialization() {
     assertTrue(Double.isNaN(gson.fromJson("NaN", Double.class)));
     assertTrue(Double.isNaN(gson.fromJson("NaN", double.class)));
   }
 
-  public void testFloatNaNSerializationNotSupportedByDefault() {
+  @Test
+  void testFloatNaNSerializationNotSupportedByDefault() {
     try {
       float nan = Float.NaN;
       gson.toJson(nan);
@@ -447,19 +498,22 @@ public void testFloatNaNSerializationNotSupportedByDefault() {
     }
   }
 
-  public void testFloatNaNSerialization() {
+  @Test
+  void testFloatNaNSerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     float nan = Float.NaN;
     assertEquals("NaN", gson.toJson(nan));
     assertEquals("NaN", gson.toJson(Float.NaN));
   }
 
-  public void testFloatNaNDeserialization() {
+  @Test
+  void testFloatNaNDeserialization() {
     assertTrue(Float.isNaN(gson.fromJson("NaN", Float.class)));
     assertTrue(Float.isNaN(gson.fromJson("NaN", float.class)));
   }
 
-  public void testBigDecimalNaNDeserializationNotSupported() {
+  @Test
+  void testBigDecimalNaNDeserializationNotSupported() {
     try {
       gson.fromJson("NaN", BigDecimal.class);
       fail("Gson should not accept NaN for deserialization by default.");
@@ -467,7 +521,8 @@ public void testBigDecimalNaNDeserializationNotSupported() {
     }
   }
 
-  public void testDoubleInfinitySerializationNotSupportedByDefault() {
+  @Test
+  void testDoubleInfinitySerializationNotSupportedByDefault() {
     try {
       double infinity = Double.POSITIVE_INFINITY;
       gson.toJson(infinity);
@@ -481,19 +536,22 @@ public void testDoubleInfinitySerializationNotSupportedByDefault() {
     }
   }
 
-  public void testDoubleInfinitySerialization() {
+  @Test
+  void testDoubleInfinitySerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     double infinity = Double.POSITIVE_INFINITY;
     assertEquals("Infinity", gson.toJson(infinity));
     assertEquals("Infinity", gson.toJson(Double.POSITIVE_INFINITY));
   }
 
-  public void testDoubleInfinityDeserialization() {
+  @Test
+  void testDoubleInfinityDeserialization() {
     assertTrue(Double.isInfinite(gson.fromJson("Infinity", Double.class)));
     assertTrue(Double.isInfinite(gson.fromJson("Infinity", double.class)));
   }
 
-  public void testFloatInfinitySerializationNotSupportedByDefault() {
+  @Test
+  void testFloatInfinitySerializationNotSupportedByDefault() {
     try {
       float infinity = Float.POSITIVE_INFINITY;
       gson.toJson(infinity);
@@ -507,19 +565,22 @@ public void testFloatInfinitySerializationNotSupportedByDefault() {
     }
   }
 
-  public void testFloatInfinitySerialization() {
+  @Test
+  void testFloatInfinitySerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     float infinity = Float.POSITIVE_INFINITY;
     assertEquals("Infinity", gson.toJson(infinity));
     assertEquals("Infinity", gson.toJson(Float.POSITIVE_INFINITY));
   }
 
-  public void testFloatInfinityDeserialization() {
+  @Test
+  void testFloatInfinityDeserialization() {
     assertTrue(Float.isInfinite(gson.fromJson("Infinity", Float.class)));
     assertTrue(Float.isInfinite(gson.fromJson("Infinity", float.class)));
   }
 
-  public void testBigDecimalInfinityDeserializationNotSupported() {
+  @Test
+  void testBigDecimalInfinityDeserializationNotSupported() {
     try {
       gson.fromJson("Infinity", BigDecimal.class);
       fail("Gson should not accept positive infinity for deserialization with BigDecimal");
@@ -527,7 +588,8 @@ public void testBigDecimalInfinityDeserializationNotSupported() {
     }
   }
 
-  public void testNegativeInfinitySerializationNotSupportedByDefault() {
+  @Test
+  void testNegativeInfinitySerializationNotSupportedByDefault() {
     try {
       double negativeInfinity = Double.NEGATIVE_INFINITY;
       gson.toJson(negativeInfinity);
@@ -541,19 +603,22 @@ public void testNegativeInfinitySerializationNotSupportedByDefault() {
     }
   }
 
-  public void testNegativeInfinitySerialization() {
+  @Test
+  void testNegativeInfinitySerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     double negativeInfinity = Double.NEGATIVE_INFINITY;
     assertEquals("-Infinity", gson.toJson(negativeInfinity));
     assertEquals("-Infinity", gson.toJson(Double.NEGATIVE_INFINITY));
   }
 
-  public void testNegativeInfinityDeserialization() {
+  @Test
+  void testNegativeInfinityDeserialization() {
     assertTrue(Double.isInfinite(gson.fromJson("-Infinity", double.class)));
     assertTrue(Double.isInfinite(gson.fromJson("-Infinity", Double.class)));
   }
 
-  public void testNegativeInfinityFloatSerializationNotSupportedByDefault() {
+  @Test
+  void testNegativeInfinityFloatSerializationNotSupportedByDefault() {
     try {
       float negativeInfinity = Float.NEGATIVE_INFINITY;
       gson.toJson(negativeInfinity);
@@ -567,19 +632,22 @@ public void testNegativeInfinityFloatSerializationNotSupportedByDefault() {
     }
   }
 
-  public void testNegativeInfinityFloatSerialization() {
+  @Test
+  void testNegativeInfinityFloatSerialization() {
     Gson gson = new GsonBuilder().serializeSpecialFloatingPointValues().create();
     float negativeInfinity = Float.NEGATIVE_INFINITY;
     assertEquals("-Infinity", gson.toJson(negativeInfinity));
     assertEquals("-Infinity", gson.toJson(Float.NEGATIVE_INFINITY));
   }
 
-  public void testNegativeInfinityFloatDeserialization() {
+  @Test
+  void testNegativeInfinityFloatDeserialization() {
     assertTrue(Float.isInfinite(gson.fromJson("-Infinity", float.class)));
     assertTrue(Float.isInfinite(gson.fromJson("-Infinity", Float.class)));
   }
 
-  public void testBigDecimalNegativeInfinityDeserializationNotSupported() {
+  @Test
+  void testBigDecimalNegativeInfinityDeserializationNotSupported() {
     try {
       gson.fromJson("-Infinity", BigDecimal.class);
       fail("Gson should not accept positive infinity for deserialization");
@@ -587,7 +655,8 @@ public void testBigDecimalNegativeInfinityDeserializationNotSupported() {
     }
   }
 
-  public void testLongAsStringSerialization() throws Exception {
+  @Test
+  void testLongAsStringSerialization() throws Exception {
     gson = new GsonBuilder().setLongSerializationPolicy(LongSerializationPolicy.STRING).create();
     String result = gson.toJson(15L);
     assertEquals("\"15\"", result);
@@ -597,7 +666,8 @@ public void testLongAsStringSerialization() throws Exception {
     assertEquals("2", result);
   }
 
-  public void testLongAsStringDeserialization() throws Exception {
+  @Test
+  void testLongAsStringDeserialization() throws Exception {
     long value = gson.fromJson("\"15\"", long.class);
     assertEquals(15, value);
 
@@ -606,7 +676,8 @@ public void testLongAsStringDeserialization() throws Exception {
     assertEquals(25, value);
   }
 
-  public void testQuotedStringSerializationAndDeserialization() throws Exception {
+  @Test
+  void testQuotedStringSerializationAndDeserialization() throws Exception {
     String value = "String Blah Blah Blah...1, 2, 3";
     String serializedForm = gson.toJson(value);
     assertEquals("\"" + value + "\"", serializedForm);
@@ -615,7 +686,8 @@ public void testQuotedStringSerializationAndDeserialization() throws Exception {
     assertEquals(value, actual);
   }
 
-  public void testUnquotedStringDeserializationFails() throws Exception {
+  @Test
+  void testUnquotedStringDeserializationFails() throws Exception {
     assertEquals("UnquotedSingleWord", gson.fromJson("UnquotedSingleWord", String.class));
 
     String value = "String Blah Blah Blah...1, 2, 3";
@@ -625,7 +697,8 @@ public void testUnquotedStringDeserializationFails() throws Exception {
     } catch (JsonSyntaxException expected) { }
   }
 
-  public void testHtmlCharacterSerialization() throws Exception {
+  @Test
+  void testHtmlCharacterSerialization() throws Exception {
     String target = "<script>var a = 12;</script>";
     String result = gson.toJson(target);
     assertFalse(result.equals('"' + target + '"'));
@@ -635,7 +708,8 @@ public void testHtmlCharacterSerialization() throws Exception {
     assertTrue(result.equals('"' + target + '"'));
   }
 
-  public void testDeserializePrimitiveWrapperAsObjectField() {
+  @Test
+  void testDeserializePrimitiveWrapperAsObjectField() {
     String json = "{i:10}";
     ClassWithIntegerField target = gson.fromJson(json, ClassWithIntegerField.class);
     assertEquals(10, target.i.intValue());
@@ -645,157 +719,180 @@ private static class ClassWithIntegerField {
     Integer i;
   }
 
-  public void testPrimitiveClassLiteral() {
+  @Test
+  void testPrimitiveClassLiteral() {
     assertEquals(1, gson.fromJson("1", int.class).intValue());
     assertEquals(1, gson.fromJson(new StringReader("1"), int.class).intValue());
     assertEquals(1, gson.fromJson(new JsonPrimitive(1), int.class).intValue());
   }
 
-  public void testDeserializeJsonObjectAsLongPrimitive() {
+  @Test
+  void testDeserializeJsonObjectAsLongPrimitive() {
     try {
       gson.fromJson("{'abc':1}", long.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsLongWrapper() {
+  @Test
+  void testDeserializeJsonArrayAsLongWrapper() {
     try {
       gson.fromJson("[1,2,3]", Long.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsInt() {
+  @Test
+  void testDeserializeJsonArrayAsInt() {
     try {
       gson.fromJson("[1, 2, 3, 4]", int.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsInteger() {
+  @Test
+  void testDeserializeJsonObjectAsInteger() {
     try {
       gson.fromJson("{}", Integer.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsShortPrimitive() {
+  @Test
+  void testDeserializeJsonObjectAsShortPrimitive() {
     try {
       gson.fromJson("{'abc':1}", short.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsShortWrapper() {
+  @Test
+  void testDeserializeJsonArrayAsShortWrapper() {
     try {
       gson.fromJson("['a','b']", Short.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsDoublePrimitive() {
+  @Test
+  void testDeserializeJsonArrayAsDoublePrimitive() {
     try {
       gson.fromJson("[1,2]", double.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsDoubleWrapper() {
+  @Test
+  void testDeserializeJsonObjectAsDoubleWrapper() {
     try {
       gson.fromJson("{'abc':1}", Double.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsFloatPrimitive() {
+  @Test
+  void testDeserializeJsonObjectAsFloatPrimitive() {
     try {
       gson.fromJson("{'abc':1}", float.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsFloatWrapper() {
+  @Test
+  void testDeserializeJsonArrayAsFloatWrapper() {
     try {
       gson.fromJson("[1,2,3]", Float.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsBytePrimitive() {
+  @Test
+  void testDeserializeJsonObjectAsBytePrimitive() {
     try {
       gson.fromJson("{'abc':1}", byte.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsByteWrapper() {
+  @Test
+  void testDeserializeJsonArrayAsByteWrapper() {
     try {
       gson.fromJson("[1,2,3,4]", Byte.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsBooleanPrimitive() {
+  @Test
+  void testDeserializeJsonObjectAsBooleanPrimitive() {
     try {
       gson.fromJson("{'abc':1}", boolean.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsBooleanWrapper() {
+  @Test
+  void testDeserializeJsonArrayAsBooleanWrapper() {
     try {
       gson.fromJson("[1,2,3,4]", Boolean.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsBigDecimal() {
+  @Test
+  void testDeserializeJsonArrayAsBigDecimal() {
     try {
       gson.fromJson("[1,2,3,4]", BigDecimal.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsBigDecimal() {
+  @Test
+  void testDeserializeJsonObjectAsBigDecimal() {
     try {
       gson.fromJson("{'a':1}", BigDecimal.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsBigInteger() {
+  @Test
+  void testDeserializeJsonArrayAsBigInteger() {
     try {
       gson.fromJson("[1,2,3,4]", BigInteger.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsBigInteger() {
+  @Test
+  void testDeserializeJsonObjectAsBigInteger() {
     try {
       gson.fromJson("{'c':2}", BigInteger.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonArrayAsNumber() {
+  @Test
+  void testDeserializeJsonArrayAsNumber() {
     try {
       gson.fromJson("[1,2,3,4]", Number.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializeJsonObjectAsNumber() {
+  @Test
+  void testDeserializeJsonObjectAsNumber() {
     try {
       gson.fromJson("{'c':2}", Number.class);
       fail();
     } catch (JsonSyntaxException expected) {}
   }
 
-  public void testDeserializingDecimalPointValueZeroSucceeds() {
+  @Test
+  void testDeserializingDecimalPointValueZeroSucceeds() {
     assertEquals(1, (int) gson.fromJson("1.0", Integer.class));
   }
 
-  public void testDeserializingNonZeroDecimalPointValuesAsIntegerFails() {
+  @Test
+  void testDeserializingNonZeroDecimalPointValuesAsIntegerFails() {
     try {
       gson.fromJson("1.02", Byte.class);
       fail();
@@ -818,7 +915,8 @@ public void testDeserializingNonZeroDecimalPointValuesAsIntegerFails() {
     }
   }
 
-  public void testDeserializingBigDecimalAsIntegerFails() {
+  @Test
+  void testDeserializingBigDecimalAsIntegerFails() {
     try {
       gson.fromJson("-122.08e-213", Integer.class);
       fail();
@@ -826,7 +924,8 @@ public void testDeserializingBigDecimalAsIntegerFails() {
     }
   }
 
-  public void testDeserializingBigIntegerAsInteger() {
+  @Test
+  void testDeserializingBigIntegerAsInteger() {
     try {
       gson.fromJson("12121211243123245845384534687435634558945453489543985435", Integer.class);
       fail();
@@ -834,7 +933,8 @@ public void testDeserializingBigIntegerAsInteger() {
     }
   }
 
-  public void testDeserializingBigIntegerAsLong() {
+  @Test
+  void testDeserializingBigIntegerAsLong() {
     try {
       gson.fromJson("12121211243123245845384534687435634558945453489543985435", Long.class);
       fail();
@@ -842,7 +942,8 @@ public void testDeserializingBigIntegerAsLong() {
     }
   }
 
-  public void testValueVeryCloseToZeroIsZero() {
+  @Test
+  void testValueVeryCloseToZeroIsZero() {
     assertEquals(0, (byte) gson.fromJson("-122.08e-2132", byte.class));
     assertEquals(0, (short) gson.fromJson("-122.08e-2132", short.class));
     assertEquals(0, (int) gson.fromJson("-122.08e-2132", int.class));
@@ -853,19 +954,22 @@ public void testValueVeryCloseToZeroIsZero() {
     assertEquals(0.0, gson.fromJson("122.08e-2132", double.class));
   }
 
-  public void testDeserializingBigDecimalAsFloat() {
+  @Test
+  void testDeserializingBigDecimalAsFloat() {
     String json = "-122.08e-2132332";
     float actual = gson.fromJson(json, float.class);
     assertEquals(-0.0f, actual);
   }
 
-  public void testDeserializingBigDecimalAsDouble() {
+  @Test
+  void testDeserializingBigDecimalAsDouble() {
     String json = "-122.08e-2132332";
     double actual = gson.fromJson(json, double.class);
     assertEquals(-0.0d, actual);
   }
 
-  public void testDeserializingBigDecimalAsBigIntegerFails() {
+  @Test
+  void testDeserializingBigDecimalAsBigIntegerFails() {
     try {
       gson.fromJson("-122.08e-213", BigInteger.class);
       fail();
@@ -873,13 +977,15 @@ public void testDeserializingBigDecimalAsBigIntegerFails() {
     }
   }
 
-  public void testDeserializingBigIntegerAsBigDecimal() {
+  @Test
+  void testDeserializingBigIntegerAsBigDecimal() {
     BigDecimal actual =
       gson.fromJson("12121211243123245845384534687435634558945453489543985435", BigDecimal.class);
     assertEquals("12121211243123245845384534687435634558945453489543985435", actual.toPlainString());
   }
 
-  public void testStringsAsBooleans() {
+  @Test
+  void testStringsAsBooleans() {
     String json = "['true', 'false', 'TRUE', 'yes', '1']";
     assertEquals(Arrays.asList(true, false, true, false, false),
         gson.<List<Boolean>>fromJson(json, new TypeToken<List<Boolean>>() {}.getType()));
diff --git a/gson/src/test/java/com/google/gson/functional/PrintFormattingTest.java b/gson/src/test/java/com/google/gson/functional/PrintFormattingTest.java
index 7dcbc23c36..c1aea3e87a 100644
--- a/gson/src/test/java/com/google/gson/functional/PrintFormattingTest.java
+++ b/gson/src/test/java/com/google/gson/functional/PrintFormattingTest.java
@@ -16,6 +16,9 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonObject;
@@ -23,11 +26,10 @@
 import com.google.gson.common.TestTypes.ClassWithTransientFields;
 import com.google.gson.common.TestTypes.Nested;
 import com.google.gson.common.TestTypes.PrimitiveArray;
-
-import junit.framework.TestCase;
-
 import java.util.ArrayList;
 import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for print formatting.
@@ -35,18 +37,18 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class PrintFormattingTest extends TestCase {
+class PrintFormattingTest {
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
   @SuppressWarnings({"unchecked", "rawtypes"})
-  public void testCompactFormattingLeavesNoWhiteSpace() {
+  @Test
+  void testCompactFormattingLeavesNoWhiteSpace() {
     List list = new ArrayList();
     list.add(new BagOfPrimitives());
     list.add(new Nested());
@@ -57,7 +59,8 @@ public void testCompactFormattingLeavesNoWhiteSpace() {
     assertContainsNoWhiteSpace(json);
   }
 
-  public void testJsonObjectWithNullValues() {
+  @Test
+  void testJsonObjectWithNullValues() {
     JsonObject obj = new JsonObject();
     obj.addProperty("field1", "value1");
     obj.addProperty("field2", (String) null);
@@ -66,7 +69,8 @@ public void testJsonObjectWithNullValues() {
     assertFalse(json.contains("field2"));
   }
 
-  public void testJsonObjectWithNullValuesSerialized() {
+  @Test
+  void testJsonObjectWithNullValuesSerialized() {
     gson = new GsonBuilder().serializeNulls().create();
     JsonObject obj = new JsonObject();
     obj.addProperty("field1", "value1");
diff --git a/gson/src/test/java/com/google/gson/functional/RawSerializationTest.java b/gson/src/test/java/com/google/gson/functional/RawSerializationTest.java
index d5e8883e78..0947efb9c8 100644
--- a/gson/src/test/java/com/google/gson/functional/RawSerializationTest.java
+++ b/gson/src/test/java/com/google/gson/functional/RawSerializationTest.java
@@ -15,42 +15,45 @@
  */
 package com.google.gson.functional;
 
-import java.util.Arrays;
-import java.util.Collection;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.Gson;
 import com.google.gson.reflect.TypeToken;
+import java.util.Arrays;
+import java.util.Collection;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests to validate serialization of parameterized types without explicit types
  *
  * @author Inderjeet Singh
  */
-public class RawSerializationTest extends TestCase {
+class RawSerializationTest {
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testCollectionOfPrimitives() {
+  @Test
+  void testCollectionOfPrimitives() {
     Collection<Integer> ints = Arrays.asList(1, 2, 3, 4, 5);
     String json = gson.toJson(ints);
     assertEquals("[1,2,3,4,5]", json);
   }
 
-  public void testCollectionOfObjects() {
+  @Test
+  void testCollectionOfObjects() {
     Collection<Foo> foos = Arrays.asList(new Foo(1), new Foo(2));
     String json = gson.toJson(foos);
     assertEquals("[{\"b\":1},{\"b\":2}]", json);
   }
 
-  public void testParameterizedObject() {
+  @Test
+  void testParameterizedObject() {
     Bar<Foo> bar = new Bar<Foo>(new Foo(1));
     String expectedJson = "{\"t\":{\"b\":1}}";
     // Ensure that serialization works without specifying the type explicitly
@@ -61,7 +64,8 @@ public void testParameterizedObject() {
     assertEquals(expectedJson, json);
   }
 
-  public void testTwoLevelParameterizedObject() {
+  @Test
+  void testTwoLevelParameterizedObject() {
     Bar<Bar<Foo>> bar = new Bar<Bar<Foo>>(new Bar<Foo>(new Foo(1)));
     String expectedJson = "{\"t\":{\"t\":{\"b\":1}}}";
     // Ensure that serialization works without specifying the type explicitly
@@ -72,7 +76,8 @@ public void testTwoLevelParameterizedObject() {
     assertEquals(expectedJson, json);
   }
 
-  public void testThreeLevelParameterizedObject() {
+  @Test
+  void testThreeLevelParameterizedObject() {
     Bar<Bar<Bar<Foo>>> bar = new Bar<Bar<Bar<Foo>>>(new Bar<Bar<Foo>>(new Bar<Foo>(new Foo(1))));
     String expectedJson = "{\"t\":{\"t\":{\"t\":{\"b\":1}}}}";
     // Ensure that serialization works without specifying the type explicitly
diff --git a/gson/src/test/java/com/google/gson/functional/ReadersWritersTest.java b/gson/src/test/java/com/google/gson/functional/ReadersWritersTest.java
index e21fb903e4..3dc2b90d2a 100644
--- a/gson/src/test/java/com/google/gson/functional/ReadersWritersTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ReadersWritersTest.java
@@ -15,16 +15,17 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonStreamParser;
 import com.google.gson.JsonSyntaxException;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
-
 import com.google.gson.reflect.TypeToken;
-import java.util.Map;
-import junit.framework.TestCase;
-
 import java.io.CharArrayReader;
 import java.io.CharArrayWriter;
 import java.io.IOException;
@@ -32,6 +33,9 @@
 import java.io.StringReader;
 import java.io.StringWriter;
 import java.io.Writer;
+import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the support of {@link Reader}s and {@link Writer}s.
@@ -39,56 +43,62 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class ReadersWritersTest extends TestCase {
+class ReadersWritersTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testWriterForSerialization() throws Exception {
+  @Test
+  void testWriterForSerialization() throws Exception {
     Writer writer = new StringWriter();
     BagOfPrimitives src = new BagOfPrimitives();
     gson.toJson(src, writer);
     assertEquals(src.getExpectedJson(), writer.toString());
   }
 
-  public void testReaderForDeserialization() throws Exception {
+  @Test
+  void testReaderForDeserialization() throws Exception {
     BagOfPrimitives expected = new BagOfPrimitives();
     Reader json = new StringReader(expected.getExpectedJson());
     BagOfPrimitives actual = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(expected, actual);
   }
 
-  public void testTopLevelNullObjectSerializationWithWriter() {
+  @Test
+  void testTopLevelNullObjectSerializationWithWriter() {
     StringWriter writer = new StringWriter();
     gson.toJson(null, writer);
     assertEquals("null", writer.toString());
   }
 
-  public void testTopLevelNullObjectDeserializationWithReader() {
+  @Test
+  void testTopLevelNullObjectDeserializationWithReader() {
     StringReader reader = new StringReader("null");
     Integer nullIntObject = gson.fromJson(reader, Integer.class);
     assertNull(nullIntObject);
   }
 
-  public void testTopLevelNullObjectSerializationWithWriterAndSerializeNulls() {
+  @Test
+  void testTopLevelNullObjectSerializationWithWriterAndSerializeNulls() {
     Gson gson = new GsonBuilder().serializeNulls().create();
     StringWriter writer = new StringWriter();
     gson.toJson(null, writer);
     assertEquals("null", writer.toString());
   }
 
-  public void testTopLevelNullObjectDeserializationWithReaderAndSerializeNulls() {
+  @Test
+  void testTopLevelNullObjectDeserializationWithReaderAndSerializeNulls() {
     Gson gson = new GsonBuilder().serializeNulls().create();
     StringReader reader = new StringReader("null");
     Integer nullIntObject = gson.fromJson(reader, Integer.class);
     assertNull(nullIntObject);
   }
 
-  public void testReadWriteTwoStrings() throws IOException {
+  @Test
+  void testReadWriteTwoStrings() throws IOException {
     Gson gson= new Gson();
     CharArrayWriter writer= new CharArrayWriter();
     writer.write(gson.toJson("one").toCharArray());
@@ -101,7 +111,8 @@ public void testReadWriteTwoStrings() throws IOException {
     assertEquals("two", actualTwo);
   }
 
-  public void testReadWriteTwoObjects() throws IOException {
+  @Test
+  void testReadWriteTwoObjects() throws IOException {
     Gson gson= new Gson();
     CharArrayWriter writer= new CharArrayWriter();
     BagOfPrimitives expectedOne = new BagOfPrimitives(1, 1, true, "one");
@@ -117,7 +128,8 @@ public void testReadWriteTwoObjects() throws IOException {
     assertFalse(parser.hasNext());
   }
 
-  public void testTypeMismatchThrowsJsonSyntaxExceptionForStrings() {
+  @Test
+  void testTypeMismatchThrowsJsonSyntaxExceptionForStrings() {
     try {
       gson.fromJson("true", new TypeToken<Map<String, String>>() {}.getType());
       fail();
@@ -125,7 +137,8 @@ public void testTypeMismatchThrowsJsonSyntaxExceptionForStrings() {
     }
   }
 
-  public void testTypeMismatchThrowsJsonSyntaxExceptionForReaders() {
+  @Test
+  void testTypeMismatchThrowsJsonSyntaxExceptionForReaders() {
     try {
       gson.fromJson(new StringReader("true"), new TypeToken<Map<String, String>>() {}.getType());
       fail();
diff --git a/gson/src/test/java/com/google/gson/functional/ReflectionAccessTest.java b/gson/src/test/java/com/google/gson/functional/ReflectionAccessTest.java
index ece351240a..9826dce3e7 100644
--- a/gson/src/test/java/com/google/gson/functional/ReflectionAccessTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ReflectionAccessTest.java
@@ -1,13 +1,14 @@
 package com.google.gson.functional;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonIOException;
+import com.google.gson.JsonSyntaxException;
 import com.google.gson.TypeAdapter;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
@@ -18,9 +19,9 @@
 import java.security.Permission;
 import java.util.Collections;
 import java.util.concurrent.atomic.AtomicBoolean;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
-public class ReflectionAccessTest {
+class ReflectionAccessTest {
   @SuppressWarnings("unused")
   private static class ClassWithPrivateMembers {
     private String s;
@@ -36,7 +37,7 @@ private static Class<?> loadClassWithDifferentClassLoader(Class<?> c) throws Exc
   }
 
   @Test
-  public void testRestrictiveSecurityManager() throws Exception {
+  void testRestrictiveSecurityManager() throws Exception {
     // Must use separate class loader, otherwise permission is not checked, see Class.getDeclaredFields()
     Class<?> clazz = loadClassWithDifferentClassLoader(ClassWithPrivateMembers.class);
 
@@ -103,7 +104,7 @@ public Object read(JsonReader in) throws IOException {
    * <p>See https://github.com/google/gson/issues/1875
    */
   @Test
-  public void testSerializeInternalImplementationObject() {
+  void testSerializeInternalImplementationObject() {
     Gson gson = new Gson();
     String json = gson.toJson(Collections.emptyList());
     assertEquals("[]", json);
@@ -113,6 +114,8 @@ public void testSerializeInternalImplementationObject() {
     try {
       gson.fromJson("{}", internalClass);
       fail("Missing exception; test has to be run with `--illegal-access=deny`");
+    } catch (JsonSyntaxException unexpected) {
+      fail("Unexpected exception type; test has to be run with `--illegal-access=deny`", unexpected);
     } catch (JsonIOException expected) {
       assertTrue(expected.getMessage().startsWith(
           "Failed making constructor 'java.util.Collections$EmptyList#EmptyList()' accessible; "
diff --git a/gson/src/test/java/com/google/gson/functional/ReusedTypeVariablesFullyResolveTest.java b/gson/src/test/java/com/google/gson/functional/ReusedTypeVariablesFullyResolveTest.java
index 10c7c6db1d..311ed1d9e1 100644
--- a/gson/src/test/java/com/google/gson/functional/ReusedTypeVariablesFullyResolveTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ReusedTypeVariablesFullyResolveTest.java
@@ -1,34 +1,34 @@
 package com.google.gson.functional;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-import org.junit.Before;
-import org.junit.Test;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Set;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * This test covers the scenario described in #1390 where a type variable needs to be used
  * by a type definition multiple times.  Both type variable references should resolve to the
  * same underlying concrete type.
  */
-public class ReusedTypeVariablesFullyResolveTest {
+class ReusedTypeVariablesFullyResolveTest {
 
   private Gson gson;
 
-  @Before
-  public void setUp() {
+  @BeforeEach
+  void setUp() {
     gson = new GsonBuilder().create();
   }
 
   @SuppressWarnings("ConstantConditions") // The instances were being unmarshaled as Strings instead of TestEnums
   @Test
-  public void testGenericsPreservation() {
+  void testGenericsPreservation() {
     TestEnumSetCollection withSet = gson.fromJson("{\"collection\":[\"ONE\",\"THREE\"]}", TestEnumSetCollection.class);
     Iterator<TestEnum> iterator = withSet.collection.iterator();
     assertNotNull(withSet);
diff --git a/gson/src/test/java/com/google/gson/functional/RuntimeTypeAdapterFactoryFunctionalTest.java b/gson/src/test/java/com/google/gson/functional/RuntimeTypeAdapterFactoryFunctionalTest.java
index 1284e2c9b6..a5f2925f2a 100644
--- a/gson/src/test/java/com/google/gson/functional/RuntimeTypeAdapterFactoryFunctionalTest.java
+++ b/gson/src/test/java/com/google/gson/functional/RuntimeTypeAdapterFactoryFunctionalTest.java
@@ -15,11 +15,7 @@
  */
 package com.google.gson.functional;
 
-import java.io.IOException;
-import java.util.LinkedHashMap;
-import java.util.Map;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.Gson;
 import com.google.gson.JsonElement;
@@ -33,11 +29,15 @@
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for the RuntimeTypeAdapterFactory feature in extras.
  */
-public final class RuntimeTypeAdapterFactoryFunctionalTest extends TestCase {
+class RuntimeTypeAdapterFactoryFunctionalTest {
 
   private final Gson gson = new Gson();
 
@@ -45,7 +45,8 @@ public final class RuntimeTypeAdapterFactoryFunctionalTest extends TestCase {
    * This test also ensures that {@link TypeAdapterFactory} registered through {@link JsonAdapter}
    * work correctly for {@link Gson#getDelegateAdapter(TypeAdapterFactory, TypeToken)}.
    */
-  public void testSubclassesAutomaticallySerialized() throws Exception {
+  @Test
+  void testSubclassesAutomaticallySerialized() throws Exception {
     Shape shape = new Circle(25);
     String json = gson.toJson(shape);
     shape = gson.fromJson(json, Shape.class);
@@ -71,7 +72,7 @@ public JsonAdapterFactory() {
     }
   }
 
-  public enum ShapeType {
+  enum ShapeType {
     SQUARE, CIRCLE
   }
 
diff --git a/gson/src/test/java/com/google/gson/functional/SecurityTest.java b/gson/src/test/java/com/google/gson/functional/SecurityTest.java
index aa1c2d4517..16a5762bda 100644
--- a/gson/src/test/java/com/google/gson/functional/SecurityTest.java
+++ b/gson/src/test/java/com/google/gson/functional/SecurityTest.java
@@ -16,18 +16,21 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Tests for security-related aspects of Gson
- * 
+ *
  * @author Inderjeet Singh
  */
-public class SecurityTest extends TestCase {
+class SecurityTest {
   /**
    * Keep this in sync with Gson.JSON_NON_EXECUTABLE_PREFIX
    */
@@ -35,52 +38,56 @@ public class SecurityTest extends TestCase {
 
   private GsonBuilder gsonBuilder;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gsonBuilder = new GsonBuilder();
   }
 
-  public void testNonExecutableJsonSerialization() {
+  @Test
+  void testNonExecutableJsonSerialization() {
     Gson gson = gsonBuilder.generateNonExecutableJson().create();
     String json = gson.toJson(new BagOfPrimitives());
     assertTrue(json.startsWith(JSON_NON_EXECUTABLE_PREFIX));
   }
-  
-  public void testNonExecutableJsonDeserialization() {
+
+  @Test
+  void testNonExecutableJsonDeserialization() {
     String json = JSON_NON_EXECUTABLE_PREFIX + "{longValue:1}";
     Gson gson = gsonBuilder.create();
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(1, target.longValue);
   }
-  
-  public void testJsonWithNonExectuableTokenSerialization() {
+
+  @Test
+  void testJsonWithNonExectuableTokenSerialization() {
     Gson gson = gsonBuilder.generateNonExecutableJson().create();
     String json = gson.toJson(JSON_NON_EXECUTABLE_PREFIX);
     assertTrue(json.contains(")]}'\n"));
   }
-  
+
   /**
    *  Gson should be able to deserialize a stream with non-exectuable token even if it is created
    *  without {@link GsonBuilder#generateNonExecutableJson()}.
    */
-  public void testJsonWithNonExectuableTokenWithRegularGsonDeserialization() {
+  @Test
+  void testJsonWithNonExectuableTokenWithRegularGsonDeserialization() {
     Gson gson = gsonBuilder.create();
     String json = JSON_NON_EXECUTABLE_PREFIX + "{stringValue:')]}\\u0027\\n'}";
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(")]}'\n", target.stringValue);
-  }  
-  
+  }
+
   /**
    *  Gson should be able to deserialize a stream with non-exectuable token if it is created
    *  with {@link GsonBuilder#generateNonExecutableJson()}.
    */
-  public void testJsonWithNonExectuableTokenWithConfiguredGsonDeserialization() {
-    // Gson should be able to deserialize a stream with non-exectuable token even if it is created 
+  @Test
+  void testJsonWithNonExectuableTokenWithConfiguredGsonDeserialization() {
+    // Gson should be able to deserialize a stream with non-exectuable token even if it is created
     Gson gson = gsonBuilder.generateNonExecutableJson().create();
     String json = JSON_NON_EXECUTABLE_PREFIX + "{intValue:2,stringValue:')]}\\u0027\\n'}";
     BagOfPrimitives target = gson.fromJson(json, BagOfPrimitives.class);
     assertEquals(")]}'\n", target.stringValue);
     assertEquals(2, target.intValue);
-  }  
+  }
 }
diff --git a/gson/src/test/java/com/google/gson/functional/SerializedNameTest.java b/gson/src/test/java/com/google/gson/functional/SerializedNameTest.java
index 0314ae0af7..644c413ebe 100644
--- a/gson/src/test/java/com/google/gson/functional/SerializedNameTest.java
+++ b/gson/src/test/java/com/google/gson/functional/SerializedNameTest.java
@@ -15,21 +15,24 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.annotations.SerializedName;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public final class SerializedNameTest extends TestCase {
+class SerializedNameTest {
   private final Gson gson = new Gson();
 
-  public void testFirstNameIsChosenForSerialization() {
+  @Test
+  void testFirstNameIsChosenForSerialization() {
     MyClass target = new MyClass("v1", "v2");
     // Ensure name1 occurs exactly once, and name2 and name3 don't appear
     assertEquals("{\"name\":\"v1\",\"name1\":\"v2\"}", gson.toJson(target));
   }
 
-  public void testMultipleNamesDeserializedCorrectly() {
+  @Test
+  void testMultipleNamesDeserializedCorrectly() {
     assertEquals("v1", gson.fromJson("{'name':'v1'}", MyClass.class).a);
 
     // Both name1 and name2 gets deserialized to b
@@ -38,7 +41,8 @@ public void testMultipleNamesDeserializedCorrectly() {
     assertEquals("v3", gson.fromJson("{'name3':'v3'}", MyClass.class).b);
   }
 
-  public void testMultipleNamesInTheSameString() {
+  @Test
+  void testMultipleNamesInTheSameString() {
     // The last value takes precedence
     assertEquals("v3", gson.fromJson("{'name1':'v1','name2':'v2','name3':'v3'}", MyClass.class).b);
   }
diff --git a/gson/src/test/java/com/google/gson/functional/StreamingTypeAdaptersTest.java b/gson/src/test/java/com/google/gson/functional/StreamingTypeAdaptersTest.java
index 45e85342c8..2082567bca 100644
--- a/gson/src/test/java/com/google/gson/functional/StreamingTypeAdaptersTest.java
+++ b/gson/src/test/java/com/google/gson/functional/StreamingTypeAdaptersTest.java
@@ -16,6 +16,11 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonArray;
@@ -33,15 +38,16 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class StreamingTypeAdaptersTest extends TestCase {
+class StreamingTypeAdaptersTest {
   private Gson miniGson = new GsonBuilder().create();
   private TypeAdapter<Truck> truckAdapter = miniGson.getAdapter(Truck.class);
   private TypeAdapter<Map<String, Double>> mapAdapter
       = miniGson.getAdapter(new TypeToken<Map<String, Double>>() {});
 
-  public void testSerialize() {
+  @Test
+  void testSerialize() {
     Truck truck = new Truck();
     truck.passengers = Arrays.asList(new Person("Jesse", 29), new Person("Jodie", 29));
     truck.horsePower = 300;
@@ -51,7 +57,8 @@ public void testSerialize() {
         truckAdapter.toJson(truck).replace('\"', '\''));
   }
 
-  public void testDeserialize() throws IOException {
+  @Test
+  void testDeserialize() throws IOException {
     String json = "{'horsePower':300.0,"
         + "'passengers':[{'age':29,'name':'Jesse'},{'age':29,'name':'Jodie'}]}";
     Truck truck = truckAdapter.fromJson(json.replace('\'', '\"'));
@@ -59,31 +66,36 @@ public void testDeserialize() throws IOException {
     assertEquals(Arrays.asList(new Person("Jesse", 29), new Person("Jodie", 29)), truck.passengers);
   }
 
-  public void testSerializeNullField() {
+  @Test
+  void testSerializeNullField() {
     Truck truck = new Truck();
     truck.passengers = null;
     assertEquals("{'horsePower':0.0,'passengers':null}",
         truckAdapter.toJson(truck).replace('\"', '\''));
   }
 
-  public void testDeserializeNullField() throws IOException {
+  @Test
+  void testDeserializeNullField() throws IOException {
     Truck truck = truckAdapter.fromJson("{'horsePower':0.0,'passengers':null}".replace('\'', '\"'));
     assertNull(truck.passengers);
   }
 
-  public void testSerializeNullObject() {
+  @Test
+  void testSerializeNullObject() {
     Truck truck = new Truck();
     truck.passengers = Arrays.asList((Person) null);
     assertEquals("{'horsePower':0.0,'passengers':[null]}",
         truckAdapter.toJson(truck).replace('\"', '\''));
   }
 
-  public void testDeserializeNullObject() throws IOException {
+  @Test
+  void testDeserializeNullObject() throws IOException {
     Truck truck = truckAdapter.fromJson("{'horsePower':0.0,'passengers':[null]}".replace('\'', '\"'));
     assertEquals(Arrays.asList((Person) null), truck.passengers);
   }
 
-  public void testSerializeWithCustomTypeAdapter() {
+  @Test
+  void testSerializeWithCustomTypeAdapter() {
     usePersonNameAdapter();
     Truck truck = new Truck();
     truck.passengers = Arrays.asList(new Person("Jesse", 29), new Person("Jodie", 29));
@@ -91,7 +103,8 @@ public void testSerializeWithCustomTypeAdapter() {
         truckAdapter.toJson(truck).replace('\"', '\''));
   }
 
-  public void testDeserializeWithCustomTypeAdapter() throws IOException {
+  @Test
+  void testDeserializeWithCustomTypeAdapter() throws IOException {
     usePersonNameAdapter();
     Truck truck = truckAdapter.fromJson("{'horsePower':0.0,'passengers':['Jesse','Jodie']}".replace('\'', '\"'));
     assertEquals(Arrays.asList(new Person("Jesse", -1), new Person("Jodie", -1)), truck.passengers);
@@ -111,51 +124,58 @@ private void usePersonNameAdapter() {
     truckAdapter = miniGson.getAdapter(Truck.class);
   }
 
-  public void testSerializeMap() {
+  @Test
+  void testSerializeMap() {
     Map<String, Double> map = new LinkedHashMap<String, Double>();
     map.put("a", 5.0);
     map.put("b", 10.0);
     assertEquals("{'a':5.0,'b':10.0}", mapAdapter.toJson(map).replace('"', '\''));
   }
 
-  public void testDeserializeMap() throws IOException {
+  @Test
+  void testDeserializeMap() throws IOException {
     Map<String, Double> map = new LinkedHashMap<String, Double>();
     map.put("a", 5.0);
     map.put("b", 10.0);
     assertEquals(map, mapAdapter.fromJson("{'a':5.0,'b':10.0}".replace('\'', '\"')));
   }
 
-  public void testSerialize1dArray() {
+  @Test
+  void testSerialize1dArray() {
     TypeAdapter<double[]> arrayAdapter = miniGson.getAdapter(new TypeToken<double[]>() {});
     assertEquals("[1.0,2.0,3.0]", arrayAdapter.toJson(new double[]{ 1.0, 2.0, 3.0 }));
   }
 
-  public void testDeserialize1dArray() throws IOException {
+  @Test
+  void testDeserialize1dArray() throws IOException {
     TypeAdapter<double[]> arrayAdapter = miniGson.getAdapter(new TypeToken<double[]>() {});
     double[] array = arrayAdapter.fromJson("[1.0,2.0,3.0]");
-    assertTrue(Arrays.toString(array), Arrays.equals(new double[]{1.0, 2.0, 3.0}, array));
+    assertArrayEquals(new double[]{1.0, 2.0, 3.0}, array);
   }
 
-  public void testSerialize2dArray() {
+  @Test
+  void testSerialize2dArray() {
     TypeAdapter<double[][]> arrayAdapter = miniGson.getAdapter(new TypeToken<double[][]>() {});
     double[][] array = { {1.0, 2.0 }, { 3.0 } };
     assertEquals("[[1.0,2.0],[3.0]]", arrayAdapter.toJson(array));
   }
 
-  public void testDeserialize2dArray() throws IOException {
+  @Test
+  void testDeserialize2dArray() throws IOException {
     TypeAdapter<double[][]> arrayAdapter = miniGson.getAdapter(new TypeToken<double[][]>() {});
     double[][] array = arrayAdapter.fromJson("[[1.0,2.0],[3.0]]");
     double[][] expected = { {1.0, 2.0 }, { 3.0 } };
-    assertTrue(Arrays.toString(array), Arrays.deepEquals(expected, array));
+    assertArrayEquals(expected, array);
   }
 
-  public void testNullSafe() {
+  @Test
+  void testNullSafe() {
     TypeAdapter<Person> typeAdapter = new TypeAdapter<Person>() {
       @Override public Person read(JsonReader in) throws IOException {
         String[] values = in.nextString().split(",");
         return new Person(values[0], Integer.parseInt(values[1]));
       }
-      public void write(JsonWriter out, Person person) throws IOException {
+      @Override public void write(JsonWriter out, Person person) throws IOException {
         out.value(person.name + "," + person.age);
       }
     };
@@ -184,7 +204,8 @@ public void write(JsonWriter out, Person person) throws IOException {
     assertEquals("jesse", truck.passengers.get(1).name);
   }
 
-  public void testSerializeRecursive() {
+  @Test
+  void testSerializeRecursive() {
     TypeAdapter<Node> nodeAdapter = miniGson.getAdapter(Node.class);
     Node root = new Node("root");
     root.left = new Node("left");
@@ -194,8 +215,9 @@ public void testSerializeRecursive() {
         + "'right':{'label':'right','left':null,'right':null}}",
         nodeAdapter.toJson(root).replace('"', '\''));
   }
-  
-  public void testFromJsonTree() {
+
+  @Test
+  void testFromJsonTree() {
     JsonObject truckObject = new JsonObject();
     truckObject.add("horsePower", new JsonPrimitive(300));
     JsonArray passengersArray = new JsonArray();
diff --git a/gson/src/test/java/com/google/gson/functional/StringTest.java b/gson/src/test/java/com/google/gson/functional/StringTest.java
index 7dcf6f0f5d..f4b131172f 100644
--- a/gson/src/test/java/com/google/gson/functional/StringTest.java
+++ b/gson/src/test/java/com/google/gson/functional/StringTest.java
@@ -1,8 +1,10 @@
 package com.google.gson.functional;
 
-import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import junit.framework.TestCase;
+import com.google.gson.Gson;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for Json serialization and deserialization of strings.
@@ -10,94 +12,107 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class StringTest extends TestCase {
+class StringTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testStringValueSerialization() throws Exception {
+  @Test
+  void testStringValueSerialization() throws Exception {
     String value = "someRandomStringValue";
     assertEquals('"' + value + '"', gson.toJson(value));
   }
 
-  public void testStringValueDeserialization() throws Exception {
+  @Test
+  void testStringValueDeserialization() throws Exception {
     String value = "someRandomStringValue";
     String actual = gson.fromJson("\"" + value + "\"", String.class);
     assertEquals(value, actual);
   }
 
-  public void testSingleQuoteInStringSerialization() throws Exception {
+  @Test
+  void testSingleQuoteInStringSerialization() throws Exception {
     String valueWithQuotes = "beforeQuote'afterQuote";
     String jsonRepresentation = gson.toJson(valueWithQuotes);
     assertEquals(valueWithQuotes, gson.fromJson(jsonRepresentation, String.class));
   }
 
-  public void testEscapedCtrlNInStringSerialization() throws Exception {
+  @Test
+  void testEscapedCtrlNInStringSerialization() throws Exception {
     String value = "a\nb";
     String json = gson.toJson(value);
     assertEquals("\"a\\nb\"", json);
   }
 
-  public void testEscapedCtrlNInStringDeserialization() throws Exception {
+  @Test
+  void testEscapedCtrlNInStringDeserialization() throws Exception {
     String json = "'a\\nb'";
     String actual = gson.fromJson(json, String.class);
     assertEquals("a\nb", actual);
   }
 
-  public void testEscapedCtrlRInStringSerialization() throws Exception {
+  @Test
+  void testEscapedCtrlRInStringSerialization() throws Exception {
     String value = "a\rb";
     String json = gson.toJson(value);
     assertEquals("\"a\\rb\"", json);
   }
 
-  public void testEscapedCtrlRInStringDeserialization() throws Exception {
+  @Test
+  void testEscapedCtrlRInStringDeserialization() throws Exception {
     String json = "'a\\rb'";
     String actual = gson.fromJson(json, String.class);
     assertEquals("a\rb", actual);
   }
 
-  public void testEscapedBackslashInStringSerialization() throws Exception {
+  @Test
+  void testEscapedBackslashInStringSerialization() throws Exception {
     String value = "a\\b";
     String json = gson.toJson(value);
     assertEquals("\"a\\\\b\"", json);
   }
 
-  public void testEscapedBackslashInStringDeserialization() throws Exception {
+  @Test
+  void testEscapedBackslashInStringDeserialization() throws Exception {
     String actual = gson.fromJson("'a\\\\b'", String.class);
     assertEquals("a\\b", actual);
   }
 
-  public void testSingleQuoteInStringDeserialization() throws Exception {
+  @Test
+  void testSingleQuoteInStringDeserialization() throws Exception {
     String value = "beforeQuote'afterQuote";
     String actual = gson.fromJson("\"" + value + "\"", String.class);
     assertEquals(value, actual);
   }
 
-  public void testEscapingQuotesInStringSerialization() throws Exception {
+  @Test
+  void testEscapingQuotesInStringSerialization() throws Exception {
     String valueWithQuotes = "beforeQuote\"afterQuote";
     String jsonRepresentation = gson.toJson(valueWithQuotes);
     String target = gson.fromJson(jsonRepresentation, String.class);
     assertEquals(valueWithQuotes, target);
   }
 
-  public void testEscapingQuotesInStringDeserialization() throws Exception {
+  @Test
+  void testEscapingQuotesInStringDeserialization() throws Exception {
     String value = "beforeQuote\\\"afterQuote";
     String actual = gson.fromJson("\"" + value + "\"", String.class);
     String expected = "beforeQuote\"afterQuote";
     assertEquals(expected, actual);
   }
 
-  public void testStringValueAsSingleElementArraySerialization() throws Exception {
+  @Test
+  void testStringValueAsSingleElementArraySerialization() throws Exception {
     String[] target = {"abc"};
     assertEquals("[\"abc\"]", gson.toJson(target));
     assertEquals("[\"abc\"]", gson.toJson(target, String[].class));
   }
 
-  public void testStringWithEscapedSlashDeserialization() {
+  @Test
+  void testStringWithEscapedSlashDeserialization() {
     String value = "/";
     String json = "'\\/'";
     String actual = gson.fromJson(json, String.class);
@@ -107,7 +122,8 @@ public void testStringWithEscapedSlashDeserialization() {
   /**
    * Created in response to http://groups.google.com/group/google-gson/browse_thread/thread/2431d4a3d0d6cb23
    */
-  public void testAssignmentCharSerialization() {
+  @Test
+  void testAssignmentCharSerialization() {
     String value = "abc=";
     String json = gson.toJson(value);
     assertEquals("\"abc\\u003d\"", json);
@@ -116,7 +132,8 @@ public void testAssignmentCharSerialization() {
   /**
    * Created in response to http://groups.google.com/group/google-gson/browse_thread/thread/2431d4a3d0d6cb23
    */
-  public void testAssignmentCharDeserialization() {
+  @Test
+  void testAssignmentCharDeserialization() {
     String json = "\"abc=\"";
     String value = gson.fromJson(json, String.class);
     assertEquals("abc=", value);
@@ -126,13 +143,15 @@ public void testAssignmentCharDeserialization() {
     assertEquals("abc=", value);
   }
 
-  public void testJavascriptKeywordsInStringSerialization() {
+  @Test
+  void testJavascriptKeywordsInStringSerialization() {
     String value = "null true false function";
     String json = gson.toJson(value);
     assertEquals("\"" + value + "\"", json);
   }
 
-  public void testJavascriptKeywordsInStringDeserialization() {
+  @Test
+  void testJavascriptKeywordsInStringDeserialization() {
     String json = "'null true false function'";
     String value = gson.fromJson(json, String.class);
     assertEquals(json.substring(1, json.length() - 1), value);
diff --git a/gson/src/test/java/com/google/gson/functional/ToNumberPolicyFunctionalTest.java b/gson/src/test/java/com/google/gson/functional/ToNumberPolicyFunctionalTest.java
index 07d99b812b..e8c3ab1181 100644
--- a/gson/src/test/java/com/google/gson/functional/ToNumberPolicyFunctionalTest.java
+++ b/gson/src/test/java/com/google/gson/functional/ToNumberPolicyFunctionalTest.java
@@ -16,12 +16,9 @@
 
 package com.google.gson.functional;
 
-import java.lang.reflect.Type;
-import java.math.BigDecimal;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.LinkedList;
-import java.util.List;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.ToNumberPolicy;
@@ -29,10 +26,17 @@
 import com.google.gson.internal.LazilyParsedNumber;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
-import junit.framework.TestCase;
+import java.lang.reflect.Type;
+import java.math.BigDecimal;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
 
-public class ToNumberPolicyFunctionalTest extends TestCase {
-  public void testDefault() {
+class ToNumberPolicyFunctionalTest {
+  @Test
+  void testDefault() {
     Gson gson = new Gson();
     assertEquals(null, gson.fromJson("null", Object.class));
     assertEquals(10D, gson.fromJson("10", Object.class));
@@ -40,7 +44,8 @@ public void testDefault() {
     assertEquals(new LazilyParsedNumber("10"), gson.fromJson("10", Number.class));
   }
 
-  public void testAsDoubles() {
+  @Test
+  void testAsDoubles() {
     Gson gson = new GsonBuilder()
         .setObjectToNumberStrategy(ToNumberPolicy.DOUBLE)
         .setNumberToNumberStrategy(ToNumberPolicy.DOUBLE)
@@ -51,7 +56,8 @@ public void testAsDoubles() {
     assertEquals(10.0, gson.fromJson("10", Number.class));
   }
 
-  public void testAsLazilyParsedNumbers() {
+  @Test
+  void testAsLazilyParsedNumbers() {
     Gson gson = new GsonBuilder()
         .setObjectToNumberStrategy(ToNumberPolicy.LAZILY_PARSED_NUMBER)
         .setNumberToNumberStrategy(ToNumberPolicy.LAZILY_PARSED_NUMBER)
@@ -62,7 +68,8 @@ public void testAsLazilyParsedNumbers() {
     assertEquals(new LazilyParsedNumber("10"), gson.fromJson("10", Number.class));
   }
 
-  public void testAsLongsOrDoubles() {
+  @Test
+  void testAsLongsOrDoubles() {
     Gson gson = new GsonBuilder()
         .setObjectToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE)
         .setNumberToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE)
@@ -75,7 +82,8 @@ public void testAsLongsOrDoubles() {
     assertEquals(10.0, gson.fromJson("10.0", Number.class));
   }
 
-  public void testAsBigDecimals() {
+  @Test
+  void testAsBigDecimals() {
     Gson gson = new GsonBuilder()
         .setObjectToNumberStrategy(ToNumberPolicy.BIG_DECIMAL)
         .setNumberToNumberStrategy(ToNumberPolicy.BIG_DECIMAL)
@@ -90,7 +98,8 @@ public void testAsBigDecimals() {
     assertEquals(new BigDecimal("1e400"), gson.fromJson("1e400", BigDecimal.class));
   }
 
-  public void testAsListOfLongsOrDoubles() {
+  @Test
+  void testAsListOfLongsOrDoubles() {
     Gson gson = new GsonBuilder()
         .setObjectToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE)
         .setNumberToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE)
@@ -107,7 +116,8 @@ public void testAsListOfLongsOrDoubles() {
     assertEquals(expected, numbers);
   }
 
-  public void testCustomStrategiesCannotAffectConcreteDeclaredNumbers() {
+  @Test
+  void testCustomStrategiesCannotAffectConcreteDeclaredNumbers() {
     ToNumberStrategy fail = new ToNumberStrategy() {
       @Override
       public Byte readNumber(JsonReader in) {
diff --git a/gson/src/test/java/com/google/gson/functional/TreeTypeAdaptersTest.java b/gson/src/test/java/com/google/gson/functional/TreeTypeAdaptersTest.java
index afcc4bccda..fb9921cfb4 100644
--- a/gson/src/test/java/com/google/gson/functional/TreeTypeAdaptersTest.java
+++ b/gson/src/test/java/com/google/gson/functional/TreeTypeAdaptersTest.java
@@ -16,13 +16,8 @@
 
 package com.google.gson.functional;
 
-import java.lang.reflect.ParameterizedType;
-import java.lang.reflect.Type;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -34,25 +29,32 @@
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import com.google.gson.reflect.TypeToken;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Collection of functional tests for DOM tree based type adapters.
  */
-public class TreeTypeAdaptersTest extends TestCase {
+class TreeTypeAdaptersTest {
   private static final Id<Student> STUDENT1_ID = new Id<Student>("5", Student.class);
   private static final Id<Student> STUDENT2_ID = new Id<Student>("6", Student.class);
   private static final Student STUDENT1 = new Student(STUDENT1_ID, "first");
   private static final Student STUDENT2 = new Student(STUDENT2_ID, "second");
   private static final Type TYPE_COURSE_HISTORY =
-    new TypeToken<Course<HistoryCourse>>(){}.getType(); 
+    new TypeToken<Course<HistoryCourse>>(){}.getType();
   private static final Id<Course<HistoryCourse>> COURSE_ID =
       new Id<Course<HistoryCourse>>("10", TYPE_COURSE_HISTORY);
 
   private Gson gson;
   private Course<HistoryCourse> course;
 
-  @Override
-  protected void setUp() {
+  @BeforeEach
+  void setUp() {
     gson = new GsonBuilder()
         .registerTypeAdapter(Id.class, new IdTreeTypeAdapter())
         .create();
@@ -60,14 +62,16 @@ protected void setUp() {
         new Assignment<HistoryCourse>(null, null), Arrays.asList(STUDENT1, STUDENT2));
   }
 
-  public void testSerializeId() {
+  @Test
+  void testSerializeId() {
     String json = gson.toJson(course, TYPE_COURSE_HISTORY);
     assertTrue(json.contains(String.valueOf(COURSE_ID.getValue())));
     assertTrue(json.contains(String.valueOf(STUDENT1_ID.getValue())));
     assertTrue(json.contains(String.valueOf(STUDENT2_ID.getValue())));
   }
 
-  public void testDeserializeId() {
+  @Test
+  void testDeserializeId() {
     String json = "{courseId:1,students:[{id:1,name:'first'},{id:6,name:'second'}],"
       + "numAssignments:4,assignment:{}}";
     Course<HistoryCourse> target = gson.fromJson(json, TYPE_COURSE_HISTORY);
diff --git a/gson/src/test/java/com/google/gson/functional/TypeAdapterPrecedenceTest.java b/gson/src/test/java/com/google/gson/functional/TypeAdapterPrecedenceTest.java
index 5f881530dc..b31303b0a2 100644
--- a/gson/src/test/java/com/google/gson/functional/TypeAdapterPrecedenceTest.java
+++ b/gson/src/test/java/com/google/gson/functional/TypeAdapterPrecedenceTest.java
@@ -16,6 +16,8 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -29,10 +31,11 @@
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
 import java.lang.reflect.Type;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
-public final class TypeAdapterPrecedenceTest extends TestCase {
-  public void testNonstreamingFollowedByNonstreaming() {
+class TypeAdapterPrecedenceTest {
+  @Test
+  void testNonstreamingFollowedByNonstreaming() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Foo.class, newSerializer("serializer 1"))
         .registerTypeAdapter(Foo.class, newSerializer("serializer 2"))
@@ -43,7 +46,8 @@ public void testNonstreamingFollowedByNonstreaming() {
     assertEquals("foo via deserializer 2", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testStreamingFollowedByStreaming() {
+  @Test
+  void testStreamingFollowedByStreaming() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Foo.class, newTypeAdapter("type adapter 1"))
         .registerTypeAdapter(Foo.class, newTypeAdapter("type adapter 2"))
@@ -52,7 +56,8 @@ public void testStreamingFollowedByStreaming() {
     assertEquals("foo via type adapter 2", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testSerializeNonstreamingTypeAdapterFollowedByStreamingTypeAdapter() {
+  @Test
+  void testSerializeNonstreamingTypeAdapterFollowedByStreamingTypeAdapter() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Foo.class, newSerializer("serializer"))
         .registerTypeAdapter(Foo.class, newDeserializer("deserializer"))
@@ -62,7 +67,8 @@ public void testSerializeNonstreamingTypeAdapterFollowedByStreamingTypeAdapter()
     assertEquals("foo via type adapter", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testStreamingFollowedByNonstreaming() {
+  @Test
+  void testStreamingFollowedByNonstreaming() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Foo.class, newTypeAdapter("type adapter"))
         .registerTypeAdapter(Foo.class, newSerializer("serializer"))
@@ -72,7 +78,8 @@ public void testStreamingFollowedByNonstreaming() {
     assertEquals("foo via deserializer", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testStreamingHierarchicalFollowedByNonstreaming() {
+  @Test
+  void testStreamingHierarchicalFollowedByNonstreaming() {
     Gson gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Foo.class, newTypeAdapter("type adapter"))
         .registerTypeAdapter(Foo.class, newSerializer("serializer"))
@@ -82,7 +89,8 @@ public void testStreamingHierarchicalFollowedByNonstreaming() {
     assertEquals("foo via deserializer", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testStreamingFollowedByNonstreamingHierarchical() {
+  @Test
+  void testStreamingFollowedByNonstreamingHierarchical() {
     Gson gson = new GsonBuilder()
         .registerTypeAdapter(Foo.class, newTypeAdapter("type adapter"))
         .registerTypeHierarchyAdapter(Foo.class, newSerializer("serializer"))
@@ -92,7 +100,8 @@ public void testStreamingFollowedByNonstreamingHierarchical() {
     assertEquals("foo via type adapter", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testStreamingHierarchicalFollowedByNonstreamingHierarchical() {
+  @Test
+  void testStreamingHierarchicalFollowedByNonstreamingHierarchical() {
     Gson gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Foo.class, newSerializer("serializer"))
         .registerTypeHierarchyAdapter(Foo.class, newDeserializer("deserializer"))
@@ -102,7 +111,8 @@ public void testStreamingHierarchicalFollowedByNonstreamingHierarchical() {
     assertEquals("foo via type adapter", gson.fromJson("foo", Foo.class).name);
   }
 
-  public void testNonstreamingHierarchicalFollowedByNonstreaming() {
+  @Test
+  void testNonstreamingHierarchicalFollowedByNonstreaming() {
     Gson gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Foo.class, newSerializer("hierarchical"))
         .registerTypeHierarchyAdapter(Foo.class, newDeserializer("hierarchical"))
diff --git a/gson/src/test/java/com/google/gson/functional/TypeHierarchyAdapterTest.java b/gson/src/test/java/com/google/gson/functional/TypeHierarchyAdapterTest.java
index 25b9c34366..688f195fb0 100644
--- a/gson/src/test/java/com/google/gson/functional/TypeHierarchyAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/functional/TypeHierarchyAdapterTest.java
@@ -16,6 +16,8 @@
 
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -27,14 +29,15 @@
 import com.google.gson.JsonSerializationContext;
 import com.google.gson.JsonSerializer;
 import java.lang.reflect.Type;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * Test that the hierarchy adapter works when subtypes are used.
  */
-public final class TypeHierarchyAdapterTest extends TestCase {
+class TypeHierarchyAdapterTest {
 
-  public void testTypeHierarchy() {
+  @Test
+  void testTypeHierarchy() {
     Manager andy = new Manager();
     andy.userid = "andy";
     andy.startDate = 2005;
@@ -116,7 +119,8 @@ public void testTypeHierarchy() {
         ((Manager) company.ceo.minions[2]).minions[1].userid);
   }
 
-  public void testRegisterSuperTypeFirst() {
+  @Test
+  void testRegisterSuperTypeFirst() {
     Gson gson = new GsonBuilder()
         .registerTypeHierarchyAdapter(Employee.class, new EmployeeAdapter())
         .registerTypeHierarchyAdapter(Manager.class, new ManagerAdapter())
@@ -132,7 +136,8 @@ public void testRegisterSuperTypeFirst() {
   }
 
   /** This behaviour changed in Gson 2.1; it used to throw. */
-  public void testRegisterSubTypeFirstAllowed() {
+  @Test
+  void testRegisterSubTypeFirstAllowed() {
     new GsonBuilder()
         .registerTypeHierarchyAdapter(Manager.class, new ManagerAdapter())
         .registerTypeHierarchyAdapter(Employee.class, new EmployeeAdapter())
diff --git a/gson/src/test/java/com/google/gson/functional/TypeVariableTest.java b/gson/src/test/java/com/google/gson/functional/TypeVariableTest.java
index 2d7503eb31..496855c103 100644
--- a/gson/src/test/java/com/google/gson/functional/TypeVariableTest.java
+++ b/gson/src/test/java/com/google/gson/functional/TypeVariableTest.java
@@ -15,17 +15,17 @@
  */
 package com.google.gson.functional;
 
-import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import com.google.gson.Gson;
 import com.google.gson.reflect.TypeToken;
 import java.lang.reflect.Type;
-import java.util.Arrays;
-import junit.framework.TestCase;
-
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional test for Gson serialization and deserialization of
@@ -33,9 +33,10 @@
  *
  * @author Joel Leitch
  */
-public class TypeVariableTest extends TestCase {
+class TypeVariableTest {
 
-  public void testAdvancedTypeVariables() throws Exception {
+  @Test
+  void testAdvancedTypeVariables() throws Exception {
     Gson gson = new Gson();
     Bar bar1 = new Bar("someString", 1, true);
     ArrayList<Integer> arrayList = new ArrayList<Integer>();
@@ -50,7 +51,8 @@ public void testAdvancedTypeVariables() throws Exception {
     assertEquals(bar1, bar2);
   }
 
-  public void testTypeVariablesViaTypeParameter() throws Exception {
+  @Test
+  void testTypeVariablesViaTypeParameter() throws Exception {
     Gson gson = new Gson();
     Foo<String, Integer> original = new Foo<String, Integer>("e", 5, false);
     original.map.put("f", Arrays.asList(6, 7));
@@ -61,7 +63,8 @@ public void testTypeVariablesViaTypeParameter() throws Exception {
     assertEquals(original, gson.<Foo<String, Integer>>fromJson(json, type));
   }
 
-  public void testBasicTypeVariables() throws Exception {
+  @Test
+  void testBasicTypeVariables() throws Exception {
     Gson gson = new Gson();
     Blue blue1 = new Blue(true);
     String json = gson.toJson(blue1);
@@ -70,7 +73,7 @@ public void testBasicTypeVariables() throws Exception {
     assertEquals(blue1, blue2);
   }
 
-  public static class Blue extends Red<Boolean> {
+  static class Blue extends Red<Boolean> {
     public Blue() {
       super(false);
     }
@@ -90,7 +93,7 @@ public boolean equals(Object o) {
     }
   }
 
-  public static class Red<S> {
+  static class Red<S> {
     protected S redField;
 
     public Red() {}
@@ -100,7 +103,7 @@ public Red(S redField) {
     }
   }
 
-  public static class Foo<S, T> extends Red<Boolean> {
+  static class Foo<S, T> extends Red<Boolean> {
     private S someSField;
     private T someTField;
     public final Map<S, List<T>> map = new HashMap<S, List<T>>();
@@ -128,7 +131,7 @@ public boolean equals(Object o) {
     }
   }
 
-  public static class Bar extends Foo<String, Integer> {
+  static class Bar extends Foo<String, Integer> {
     public Bar() {
       this("", 0, false);
     }
diff --git a/gson/src/test/java/com/google/gson/functional/UncategorizedTest.java b/gson/src/test/java/com/google/gson/functional/UncategorizedTest.java
index 0ac0380357..9fa71e5f59 100644
--- a/gson/src/test/java/com/google/gson/functional/UncategorizedTest.java
+++ b/gson/src/test/java/com/google/gson/functional/UncategorizedTest.java
@@ -15,6 +15,11 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -23,13 +28,12 @@
 import com.google.gson.JsonParseException;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 import com.google.gson.common.TestTypes.ClassOverridingEquals;
-
 import com.google.gson.reflect.TypeToken;
+import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.List;
-import junit.framework.TestCase;
-
-import java.lang.reflect.Type;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests that do not fall neatly into any of the existing classification.
@@ -37,17 +41,17 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class UncategorizedTest extends TestCase {
+class UncategorizedTest {
 
   private Gson gson = null;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
 
-  public void testInvalidJsonDeserializationFails() throws Exception {
+  @Test
+  void testInvalidJsonDeserializationFails() throws Exception {
     try {
       gson.fromJson("adfasdf1112,,,\":", BagOfPrimitives.class);
       fail("Bad JSON should throw a ParseException");
@@ -59,7 +63,8 @@ public void testInvalidJsonDeserializationFails() throws Exception {
     } catch (JsonParseException expected) { }
   }
 
-  public void testObjectEqualButNotSameSerialization() throws Exception {
+  @Test
+  void testObjectEqualButNotSameSerialization() throws Exception {
     ClassOverridingEquals objA = new ClassOverridingEquals();
     ClassOverridingEquals objB = new ClassOverridingEquals();
     objB.ref = objA;
@@ -67,12 +72,14 @@ public void testObjectEqualButNotSameSerialization() throws Exception {
     assertEquals(objB.getExpectedJson(), json);
   }
 
-  public void testStaticFieldsAreNotSerialized() {
+  @Test
+  void testStaticFieldsAreNotSerialized() {
     BagOfPrimitives target = new BagOfPrimitives();
     assertFalse(gson.toJson(target).contains("DEFAULT_VALUE"));
   }
 
-  public void testGsonInstanceReusableForSerializationAndDeserialization() {
+  @Test
+  void testGsonInstanceReusableForSerializationAndDeserialization() {
     BagOfPrimitives bag = new BagOfPrimitives();
     String json = gson.toJson(bag);
     BagOfPrimitives deserialized = gson.fromJson(json, BagOfPrimitives.class);
@@ -84,7 +91,8 @@ public void testGsonInstanceReusableForSerializationAndDeserialization() {
    * base class object. For a motivation for this test, see Issue 37 and
    * http://groups.google.com/group/google-gson/browse_thread/thread/677d56e9976d7761
    */
-  public void testReturningDerivedClassesDuringDeserialization() {
+  @Test
+  void testReturningDerivedClassesDuringDeserialization() {
     Gson gson = new GsonBuilder().registerTypeAdapter(Base.class, new BaseTypeAdapter()).create();
     String json = "{\"opType\":\"OP1\"}";
     Base base = gson.fromJson(json, Base.class);
@@ -101,7 +109,8 @@ public void testReturningDerivedClassesDuringDeserialization() {
    * Test that trailing whitespace is ignored.
    * http://code.google.com/p/google-gson/issues/detail?id=302
    */
-  public void testTrailingWhitespace() throws Exception {
+  @Test
+  void testTrailingWhitespace() throws Exception {
     List<Integer> integers = gson.fromJson("[1,2,3]  \n\n  ",
         new TypeToken<List<Integer>>() {}.getType());
     assertEquals(Arrays.asList(1, 2, 3), integers);
diff --git a/gson/src/test/java/com/google/gson/functional/VersioningTest.java b/gson/src/test/java/com/google/gson/functional/VersioningTest.java
index 2416fc06d7..6b69570b45 100644
--- a/gson/src/test/java/com/google/gson/functional/VersioningTest.java
+++ b/gson/src/test/java/com/google/gson/functional/VersioningTest.java
@@ -15,13 +15,18 @@
  */
 package com.google.gson.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.annotations.Since;
 import com.google.gson.annotations.Until;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
-
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for versioning support in Gson.
@@ -29,7 +34,7 @@
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class VersioningTest extends TestCase {
+class VersioningTest {
   private static final int A = 0;
   private static final int B = 1;
   private static final int C = 2;
@@ -37,13 +42,13 @@ public class VersioningTest extends TestCase {
 
   private GsonBuilder builder;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     builder = new GsonBuilder();
   }
 
-  public void testVersionedUntilSerialization() {
+  @Test
+  void testVersionedUntilSerialization() {
     Version1 target = new Version1();
     Gson gson = builder.setVersion(1.29).create();
     String json = gson.toJson(target);
@@ -54,21 +59,24 @@ public void testVersionedUntilSerialization() {
     assertFalse(json.contains("\"a\":" + A));
   }
 
-  public void testVersionedUntilDeserialization() {
+  @Test
+  void testVersionedUntilDeserialization() {
     Gson gson = builder.setVersion(1.3).create();
     String json = "{\"a\":3,\"b\":4,\"c\":5}";
     Version1 version1 = gson.fromJson(json, Version1.class);
     assertEquals(A, version1.a);
   }
 
-  public void testVersionedClassesSerialization() {
+  @Test
+  void testVersionedClassesSerialization() {
     Gson gson = builder.setVersion(1.0).create();
     String json1 = gson.toJson(new Version1());
     String json2 = gson.toJson(new Version1_1());
     assertEquals(json1, json2);
   }
 
-  public void testVersionedClassesDeserialization() {
+  @Test
+  void testVersionedClassesDeserialization() {
     Gson gson = builder.setVersion(1.0).create();
     String json = "{\"a\":3,\"b\":4,\"c\":5}";
     Version1 version1 = gson.fromJson(json, Version1.class);
@@ -80,12 +88,14 @@ public void testVersionedClassesDeserialization() {
     assertEquals(C, version1_1.c);
   }
 
-  public void testIgnoreLaterVersionClassSerialization() {
+  @Test
+  void testIgnoreLaterVersionClassSerialization() {
     Gson gson = builder.setVersion(1.0).create();
     assertEquals("null", gson.toJson(new Version1_2()));
   }
 
-  public void testIgnoreLaterVersionClassDeserialization() {
+  @Test
+  void testIgnoreLaterVersionClassDeserialization() {
     Gson gson = builder.setVersion(1.0).create();
     String json = "{\"a\":3,\"b\":4,\"c\":5,\"d\":6}";
     Version1_2 version1_2 = gson.fromJson(json, Version1_2.class);
@@ -94,13 +104,15 @@ public void testIgnoreLaterVersionClassDeserialization() {
     assertNull(version1_2);
   }
 
-  public void testVersionedGsonWithUnversionedClassesSerialization() {
+  @Test
+  void testVersionedGsonWithUnversionedClassesSerialization() {
     Gson gson = builder.setVersion(1.0).create();
     BagOfPrimitives target = new BagOfPrimitives(10, 20, false, "stringValue");
     assertEquals(target.getExpectedJson(), gson.toJson(target));
   }
 
-  public void testVersionedGsonWithUnversionedClassesDeserialization() {
+  @Test
+  void testVersionedGsonWithUnversionedClassesDeserialization() {
     Gson gson = builder.setVersion(1.0).create();
     String json = "{\"longValue\":10,\"intValue\":20,\"booleanValue\":false}";
 
@@ -112,7 +124,8 @@ public void testVersionedGsonWithUnversionedClassesDeserialization() {
     assertEquals(expected, actual);
   }
 
-  public void testVersionedGsonMixingSinceAndUntilSerialization() {
+  @Test
+  void testVersionedGsonMixingSinceAndUntilSerialization() {
     Gson gson = builder.setVersion(1.0).create();
     SinceUntilMixing target = new SinceUntilMixing();
     String json = gson.toJson(target);
@@ -127,7 +140,8 @@ public void testVersionedGsonMixingSinceAndUntilSerialization() {
     assertFalse(json.contains("\"b\":" + B));
   }
 
-  public void testVersionedGsonMixingSinceAndUntilDeserialization() {
+  @Test
+  void testVersionedGsonMixingSinceAndUntilDeserialization() {
     String json = "{\"a\":5,\"b\":6}";
     Gson gson = builder.setVersion(1.0).create();
     SinceUntilMixing result = gson.fromJson(json, SinceUntilMixing.class);
diff --git a/gson/src/test/java/com/google/gson/internal/GsonBuildConfigTest.java b/gson/src/test/java/com/google/gson/internal/GsonBuildConfigTest.java
index dc39bc02df..3ba50a3cf3 100644
--- a/gson/src/test/java/com/google/gson/internal/GsonBuildConfigTest.java
+++ b/gson/src/test/java/com/google/gson/internal/GsonBuildConfigTest.java
@@ -15,19 +15,19 @@
  */
 package com.google.gson.internal;
 
-import static org.junit.Assert.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit tests for {@code GsonBuildConfig}
  *
  * @author Inderjeet Singh
  */
-public class GsonBuildConfigTest {
+class GsonBuildConfigTest {
 
   @Test
-  public void testEnsureGsonBuildConfigGetsUpdatedToMavenVersion() {
+  void testEnsureGsonBuildConfigGetsUpdatedToMavenVersion() {
     assertFalse("${project.version}".equals(GsonBuildConfig.VERSION));
   }
 }
diff --git a/gson/src/test/java/com/google/gson/internal/GsonTypesTest.java b/gson/src/test/java/com/google/gson/internal/GsonTypesTest.java
index c80700bde4..5d13f2919b 100644
--- a/gson/src/test/java/com/google/gson/internal/GsonTypesTest.java
+++ b/gson/src/test/java/com/google/gson/internal/GsonTypesTest.java
@@ -16,15 +16,19 @@
 
 package com.google.gson.internal;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.List;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public final class GsonTypesTest extends TestCase {
+class GsonTypesTest {
 
-  public void testNewParameterizedTypeWithoutOwner() throws Exception {
+  @Test
+  void testNewParameterizedTypeWithoutOwner() throws Exception {
     // List<A>. List is a top-level class
     Type type = $Gson$Types.newParameterizedTypeWithOwner(null, List.class, A.class);
     assertEquals(A.class, getFirstTypeArgument(type));
@@ -46,7 +50,8 @@ final class D {
     assertEquals(D.class, getFirstTypeArgument(type));
   }
 
-  public void testGetFirstTypeArgument() throws Exception {
+  @Test
+  void testGetFirstTypeArgument() throws Exception {
     assertNull(getFirstTypeArgument(A.class));
 
     Type type = $Gson$Types.newParameterizedTypeWithOwner(null, A.class, B.class, C.class);
@@ -64,7 +69,7 @@ private static final class C {
    * Given a parameterized type A&lt;B,C&gt;, returns B. If the specified type is not
    * a generic type, returns null.
    */
-  public static Type getFirstTypeArgument(Type type) throws Exception {
+  private static Type getFirstTypeArgument(Type type) throws Exception {
     if (!(type instanceof ParameterizedType)) return null;
     ParameterizedType ptype = (ParameterizedType) type;
     Type[] actualTypeArguments = ptype.getActualTypeArguments();
diff --git a/gson/src/test/java/com/google/gson/internal/JavaVersionTest.java b/gson/src/test/java/com/google/gson/internal/JavaVersionTest.java
index 54b62862ca..7b60a5efe7 100644
--- a/gson/src/test/java/com/google/gson/internal/JavaVersionTest.java
+++ b/gson/src/test/java/com/google/gson/internal/JavaVersionTest.java
@@ -15,35 +15,36 @@
  */
 package com.google.gson.internal;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 /**
  * Unit and functional tests for {@link JavaVersion}
  *
  * @author Inderjeet Singh
  */
-public class JavaVersionTest {
+class JavaVersionTest {
   // Borrowed some of test strings from https://github.com/prestodb/presto/blob/master/presto-main/src/test/java/com/facebook/presto/server/TestJavaVersion.java
 
   @Test
-  public void testGetMajorJavaVersion() {
-    JavaVersion.getMajorJavaVersion();
+  void testGetMajorJavaVersion() {
+    assertTrue(JavaVersion.getMajorJavaVersion() >= 7);
   }
 
   @Test
-  public void testJava6() {
+  void testJava6() {
     assertEquals(6, JavaVersion.getMajorJavaVersion("1.6.0")); // http://www.oracle.com/technetwork/java/javase/version-6-141920.html
   }
 
   @Test
-  public void testJava7() {
+  void testJava7() {
     assertEquals(7, JavaVersion.getMajorJavaVersion("1.7.0")); // http://www.oracle.com/technetwork/java/javase/jdk7-naming-418744.html
   }
 
   @Test
-  public void testJava8() {
+  void testJava8() {
     assertEquals(8, JavaVersion.getMajorJavaVersion("1.8"));
     assertEquals(8, JavaVersion.getMajorJavaVersion("1.8.0"));
     assertEquals(8, JavaVersion.getMajorJavaVersion("1.8.0_131"));
@@ -56,7 +57,7 @@ public void testJava8() {
   }
 
   @Test
-  public void testJava9() {
+  void testJava9() {
     // Legacy style
     assertEquals(9, JavaVersion.getMajorJavaVersion("9.0.4")); // Oracle JDK 9
     assertEquals(9, JavaVersion.getMajorJavaVersion("9-Debian")); // Debian as reported in https://github.com/google/gson/issues/1310
@@ -68,12 +69,12 @@ public void testJava9() {
   }
 
   @Test
-  public void testJava10() {
+  void testJava10() {
     assertEquals(10, JavaVersion.getMajorJavaVersion("10.0.1")); // Oracle JDK 10.0.1
   }
 
   @Test
-  public void testUnknownVersionFormat() {
-    assertEquals(6, JavaVersion.getMajorJavaVersion("Java9")); // unknown format
+  void testUnknownVersionFormat() {
+    assertEquals(7, JavaVersion.getMajorJavaVersion("Java9")); // unknown format
   }
 }
diff --git a/gson/src/test/java/com/google/gson/internal/LazilyParsedNumberTest.java b/gson/src/test/java/com/google/gson/internal/LazilyParsedNumberTest.java
index 75e77bb55f..d1a6ae089f 100644
--- a/gson/src/test/java/com/google/gson/internal/LazilyParsedNumberTest.java
+++ b/gson/src/test/java/com/google/gson/internal/LazilyParsedNumberTest.java
@@ -15,29 +15,34 @@
  */
 package com.google.gson.internal;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public class LazilyParsedNumberTest extends TestCase {
-  public void testHashCode() {
+class LazilyParsedNumberTest {
+  @Test
+  void testHashCode() {
     LazilyParsedNumber n1 = new LazilyParsedNumber("1");
     LazilyParsedNumber n1Another = new LazilyParsedNumber("1");
     assertEquals(n1.hashCode(), n1Another.hashCode());
   }
 
-  public void testEquals() {
+  @Test
+  void testEquals() {
     LazilyParsedNumber n1 = new LazilyParsedNumber("1");
     LazilyParsedNumber n1Another = new LazilyParsedNumber("1");
     assertTrue(n1.equals(n1Another));
   }
 
-  public void testJavaSerialization() throws IOException, ClassNotFoundException {
+  @Test
+  void testJavaSerialization() throws IOException, ClassNotFoundException {
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     ObjectOutputStream objOut = new ObjectOutputStream(out);
     objOut.writeObject(new LazilyParsedNumber("123"));
diff --git a/gson/src/test/java/com/google/gson/internal/LinkedTreeMapTest.java b/gson/src/test/java/com/google/gson/internal/LinkedTreeMapTest.java
index fa8b08c3e0..7991f5b114 100644
--- a/gson/src/test/java/com/google/gson/internal/LinkedTreeMapTest.java
+++ b/gson/src/test/java/com/google/gson/internal/LinkedTreeMapTest.java
@@ -16,6 +16,13 @@
 
 package com.google.gson.internal;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import com.google.gson.common.MoreAsserts;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -27,14 +34,12 @@
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Random;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-import com.google.gson.common.MoreAsserts;
-
-public final class LinkedTreeMapTest extends TestCase {
+class LinkedTreeMapTest {
 
-  public void testIterationOrder() {
+  @Test
+  void testIterationOrder() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "android");
     map.put("c", "cola");
@@ -43,7 +48,8 @@ public void testIterationOrder() {
     assertIterationOrder(map.values(), "android", "cola", "bbq");
   }
 
-  public void testRemoveRootDoesNotDoubleUnlink() {
+  @Test
+  void testRemoveRootDoesNotDoubleUnlink() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "android");
     map.put("c", "cola");
@@ -56,7 +62,8 @@ public void testRemoveRootDoesNotDoubleUnlink() {
     assertIterationOrder(map.keySet(), "a", "c");
   }
 
-  public void testPutNullKeyFails() {
+  @Test
+  void testPutNullKeyFails() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     try {
       map.put(null, "android");
@@ -65,7 +72,8 @@ public void testPutNullKeyFails() {
     }
   }
 
-  public void testPutNonComparableKeyFails() {
+  @Test
+  void testPutNonComparableKeyFails() {
     LinkedTreeMap<Object, String> map = new LinkedTreeMap<Object, String>();
     try {
       map.put(new Object(), "android");
@@ -73,19 +81,22 @@ public void testPutNonComparableKeyFails() {
     } catch (ClassCastException expected) {}
   }
 
-  public void testContainsNonComparableKeyReturnsFalse() {
+  @Test
+  void testContainsNonComparableKeyReturnsFalse() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "android");
     assertFalse(map.containsKey(new Object()));
   }
 
-  public void testContainsNullKeyIsAlwaysFalse() {
+  @Test
+  void testContainsNullKeyIsAlwaysFalse() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "android");
     assertFalse(map.containsKey(null));
   }
 
-  public void testPutOverrides() throws Exception {
+  @Test
+  void testPutOverrides() throws Exception {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     assertNull(map.put("d", "donut"));
     assertNull(map.put("e", "eclair"));
@@ -97,14 +108,16 @@ public void testPutOverrides() throws Exception {
     assertEquals(3, map.size());
   }
 
-  public void testEmptyStringValues() {
+  @Test
+  void testEmptyStringValues() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "");
     assertTrue(map.containsKey("a"));
     assertEquals("", map.get("a"));
   }
 
-  public void testLargeSetOfRandomKeys() throws Exception {
+  @Test
+  void testLargeSetOfRandomKeys() throws Exception {
     Random random = new Random(1367593214724L);
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     String[] keys = new String[1000];
@@ -120,7 +133,8 @@ public void testLargeSetOfRandomKeys() throws Exception {
     }
   }
 
-  public void testClear() {
+  @Test
+  void testClear() {
     LinkedTreeMap<String, String> map = new LinkedTreeMap<String, String>();
     map.put("a", "android");
     map.put("c", "cola");
@@ -130,7 +144,8 @@ public void testClear() {
     assertEquals(0, map.size());
   }
 
-  public void testEqualsAndHashCode() throws Exception {
+  @Test
+  void testEqualsAndHashCode() throws Exception {
     LinkedTreeMap<String, Integer> map1 = new LinkedTreeMap<String, Integer>();
     map1.put("A", 1);
     map1.put("B", 2);
@@ -146,7 +161,8 @@ public void testEqualsAndHashCode() throws Exception {
     MoreAsserts.assertEqualsAndHashCode(map1, map2);
   }
 
-  public void testJavaSerialization() throws IOException, ClassNotFoundException {
+  @Test
+  void testJavaSerialization() throws IOException, ClassNotFoundException {
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     ObjectOutputStream objOut = new ObjectOutputStream(out);
     Map<String, Integer> map = new LinkedTreeMap<String, Integer>();
diff --git a/gson/src/test/java/com/google/gson/internal/UnsafeAllocatorInstantiationTest.java b/gson/src/test/java/com/google/gson/internal/UnsafeAllocatorInstantiationTest.java
index 9e1807899f..b5e060ead6 100644
--- a/gson/src/test/java/com/google/gson/internal/UnsafeAllocatorInstantiationTest.java
+++ b/gson/src/test/java/com/google/gson/internal/UnsafeAllocatorInstantiationTest.java
@@ -15,28 +15,32 @@
  */
 package com.google.gson.internal;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
 
 /**
  * Test unsafe allocator instantiation
  * @author Ugljesa Jovanovic
  */
-public final class UnsafeAllocatorInstantiationTest extends TestCase {
+class UnsafeAllocatorInstantiationTest {
 
-  public interface Interface {
+  interface Interface {
   }
 
-  public static abstract class AbstractClass {
+  static abstract class AbstractClass {
   }
 
-  public static class ConcreteClass {
+  static class ConcreteClass {
   }
 
   /**
    * Ensure that the {@link java.lang.UnsupportedOperationException} is thrown when trying
    * to instantiate an interface
    */
-  public void testInterfaceInstantiation() {
+  @Test
+  void testInterfaceInstantiation() {
     UnsafeAllocator unsafeAllocator = UnsafeAllocator.create();
     try {
       unsafeAllocator.newInstance(Interface.class);
@@ -50,7 +54,8 @@ public void testInterfaceInstantiation() {
    * Ensure that the {@link java.lang.UnsupportedOperationException} is thrown when trying
    * to instantiate an abstract class
    */
-  public void testAbstractClassInstantiation() {
+  @Test
+  void testAbstractClassInstantiation() {
     UnsafeAllocator unsafeAllocator = UnsafeAllocator.create();
     try {
       unsafeAllocator.newInstance(AbstractClass.class);
@@ -63,7 +68,8 @@ public void testAbstractClassInstantiation() {
   /**
    * Ensure that no exception is thrown when trying to instantiate a concrete class
    */
-  public void testConcreteClassInstantiation() {
+  @Test
+  void testConcreteClassInstantiation() {
     UnsafeAllocator unsafeAllocator = UnsafeAllocator.create();
     try {
       unsafeAllocator.newInstance(ConcreteClass.class);
diff --git a/gson/src/test/java/com/google/gson/internal/bind/DefaultDateTypeAdapterTest.java b/gson/src/test/java/com/google/gson/internal/bind/DefaultDateTypeAdapterTest.java
index 3d1ec7f794..bdec75bbb6 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/DefaultDateTypeAdapterTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/DefaultDateTypeAdapterTest.java
@@ -16,12 +16,10 @@
 
 package com.google.gson.internal.bind;
 
-import java.io.IOException;
-import java.text.DateFormat;
-import java.text.SimpleDateFormat;
-import java.util.Date;
-import java.util.Locale;
-import java.util.TimeZone;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.gson.Gson;
 import com.google.gson.TypeAdapter;
@@ -29,21 +27,28 @@
 import com.google.gson.internal.JavaVersion;
 import com.google.gson.internal.bind.DefaultDateTypeAdapter.DateType;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
+import java.io.IOException;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+import org.junit.jupiter.api.Test;
 
 /**
  * A simple unit test for the {@link DefaultDateTypeAdapter} class.
  *
  * @author Joel Leitch
  */
-public class DefaultDateTypeAdapterTest extends TestCase {
+class DefaultDateTypeAdapterTest {
 
-  public void testFormattingInEnUs() {
+  @Test
+  void testFormattingInEnUs() {
     assertFormattingAlwaysEmitsUsLocale(Locale.US);
   }
 
-  public void testFormattingInFr() {
+  @Test
+  void testFormattingInFr() {
     assertFormattingAlwaysEmitsUsLocale(Locale.FRANCE);
   }
 
@@ -75,7 +80,8 @@ private void assertFormattingAlwaysEmitsUsLocale(Locale locale) {
     }
   }
 
-  public void testParsingDatesFormattedWithSystemLocale() throws Exception {
+  @Test
+  void testParsingDatesFormattedWithSystemLocale() throws Exception {
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
     Locale defaultLocale = Locale.getDefault();
@@ -104,7 +110,8 @@ public void testParsingDatesFormattedWithSystemLocale() throws Exception {
     }
   }
 
-  public void testParsingDatesFormattedWithUsLocale() throws Exception {
+  @Test
+  void testParsingDatesFormattedWithUsLocale() throws Exception {
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
     Locale defaultLocale = Locale.getDefault();
@@ -128,7 +135,8 @@ public void testParsingDatesFormattedWithUsLocale() throws Exception {
     }
   }
 
-  public void testFormatUsesDefaultTimezone() throws Exception {
+  @Test
+  void testFormatUsesDefaultTimezone() throws Exception {
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
     Locale defaultLocale = Locale.getDefault();
@@ -144,7 +152,8 @@ public void testFormatUsesDefaultTimezone() throws Exception {
     }
   }
 
-  public void testDateDeserializationISO8601() throws Exception {
+  @Test
+  void testDateDeserializationISO8601() throws Exception {
     TypeAdapterFactory adapterFactory = DateType.DATE.createDefaultsAdapterFactory();
     assertParsed("1970-01-01T00:00:00.000Z", adapterFactory);
     assertParsed("1970-01-01T00:00Z", adapterFactory);
@@ -153,7 +162,8 @@ public void testDateDeserializationISO8601() throws Exception {
     assertParsed("1970-01-01T01:00:00+01", adapterFactory);
   }
 
-  public void testDateSerialization() throws Exception {
+  @Test
+  void testDateSerialization() throws Exception {
     int dateStyle = DateFormat.LONG;
     TypeAdapter<Date> dateTypeAdapter = dateAdapter(DateType.DATE.createAdapterFactory(dateStyle));
     DateFormat formatter = DateFormat.getDateInstance(dateStyle, Locale.US);
@@ -163,7 +173,8 @@ public void testDateSerialization() throws Exception {
     assertEquals(toLiteral(formatter.format(currentDate)), dateString);
   }
 
-  public void testDatePattern() throws Exception {
+  @Test
+  void testDatePattern() throws Exception {
     String pattern = "yyyy-MM-dd";
     TypeAdapter<Date> dateTypeAdapter = dateAdapter(DateType.DATE.createAdapterFactory(pattern));
     DateFormat formatter = new SimpleDateFormat(pattern);
@@ -173,20 +184,23 @@ public void testDatePattern() throws Exception {
     assertEquals(toLiteral(formatter.format(currentDate)), dateString);
   }
 
-  public void testInvalidDatePattern() throws Exception {
+  @Test
+  void testInvalidDatePattern() throws Exception {
     try {
       DateType.DATE.createAdapterFactory("I am a bad Date pattern....");
       fail("Invalid date pattern should fail.");
     } catch (IllegalArgumentException expected) { }
   }
 
-  public void testNullValue() throws Exception {
+  @Test
+  void testNullValue() throws Exception {
     TypeAdapter<Date> adapter = dateAdapter(DateType.DATE.createDefaultsAdapterFactory());
     assertNull(adapter.fromJson("null"));
     assertEquals("null", adapter.toJson(null));
   }
 
-  public void testUnexpectedToken() throws Exception {
+  @Test
+  void testUnexpectedToken() throws Exception {
     try {
       TypeAdapter<Date> adapter = dateAdapter(DateType.DATE.createDefaultsAdapterFactory());
       adapter.fromJson("{}");
@@ -207,8 +221,8 @@ private static void assertFormatted(String formatted, TypeAdapterFactory adapter
 
   private static void assertParsed(String date, TypeAdapterFactory adapterFactory) throws IOException {
     TypeAdapter<Date> adapter = dateAdapter(adapterFactory);
-    assertEquals(date, new Date(0), adapter.fromJson(toLiteral(date)));
-    assertEquals("ISO 8601", new Date(0), adapter.fromJson(toLiteral("1970-01-01T00:00:00Z")));
+    assertEquals(new Date(0), adapter.fromJson(toLiteral(date)), date);
+    assertEquals(new Date(0), adapter.fromJson(toLiteral("1970-01-01T00:00:00Z")), "ISO 8601");
   }
 
   private static String toLiteral(String s) {
diff --git a/gson/src/test/java/com/google/gson/internal/bind/JsonElementReaderTest.java b/gson/src/test/java/com/google/gson/internal/bind/JsonElementReaderTest.java
index 204fb3c3f5..d97b9bd311 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/JsonElementReaderTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/JsonElementReaderTest.java
@@ -16,17 +16,22 @@
 
 package com.google.gson.internal.bind;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.JsonElement;
 import com.google.gson.JsonParser;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.stream.JsonToken;
 import java.io.IOException;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 @SuppressWarnings("resource")
-public final class JsonElementReaderTest extends TestCase {
+class JsonElementReaderTest {
 
-  public void testNumbers() throws IOException {
+  @Test
+  void testNumbers() throws IOException {
     JsonElement element = JsonParser.parseString("[1, 2, 3]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -36,7 +41,8 @@ public void testNumbers() throws IOException {
     reader.endArray();
   }
 
-  public void testLenientNansAndInfinities() throws IOException {
+  @Test
+  void testLenientNansAndInfinities() throws IOException {
     JsonElement element = JsonParser.parseString("[NaN, -Infinity, Infinity]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.setLenient(true);
@@ -47,7 +53,8 @@ public void testLenientNansAndInfinities() throws IOException {
     reader.endArray();
   }
 
-  public void testStrictNansAndInfinities() throws IOException {
+  @Test
+  void testStrictNansAndInfinities() throws IOException {
     JsonElement element = JsonParser.parseString("[NaN, -Infinity, Infinity]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.setLenient(false);
@@ -73,7 +80,8 @@ public void testStrictNansAndInfinities() throws IOException {
     reader.endArray();
   }
 
-  public void testNumbersFromStrings() throws IOException {
+  @Test
+  void testNumbersFromStrings() throws IOException {
     JsonElement element = JsonParser.parseString("[\"1\", \"2\", \"3\"]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -83,7 +91,8 @@ public void testNumbersFromStrings() throws IOException {
     reader.endArray();
   }
 
-  public void testStringsFromNumbers() throws IOException {
+  @Test
+  void testStringsFromNumbers() throws IOException {
     JsonElement element = JsonParser.parseString("[1]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -91,7 +100,8 @@ public void testStringsFromNumbers() throws IOException {
     reader.endArray();
   }
 
-  public void testBooleans() throws IOException {
+  @Test
+  void testBooleans() throws IOException {
     JsonElement element = JsonParser.parseString("[true, false]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -100,7 +110,8 @@ public void testBooleans() throws IOException {
     reader.endArray();
   }
 
-  public void testNulls() throws IOException {
+  @Test
+  void testNulls() throws IOException {
     JsonElement element = JsonParser.parseString("[null,null]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -109,7 +120,8 @@ public void testNulls() throws IOException {
     reader.endArray();
   }
 
-  public void testStrings() throws IOException {
+  @Test
+  void testStrings() throws IOException {
     JsonElement element = JsonParser.parseString("[\"A\",\"B\"]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -118,7 +130,8 @@ public void testStrings() throws IOException {
     reader.endArray();
   }
 
-  public void testArray() throws IOException {
+  @Test
+  void testArray() throws IOException {
     JsonElement element = JsonParser.parseString("[1, 2, 3]");
     JsonTreeReader reader = new JsonTreeReader(element);
     assertEquals(JsonToken.BEGIN_ARRAY, reader.peek());
@@ -134,7 +147,8 @@ public void testArray() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testObject() throws IOException {
+  @Test
+  void testObject() throws IOException {
     JsonElement element = JsonParser.parseString("{\"A\": 1, \"B\": 2}");
     JsonTreeReader reader = new JsonTreeReader(element);
     assertEquals(JsonToken.BEGIN_OBJECT, reader.peek());
@@ -152,14 +166,16 @@ public void testObject() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testEmptyArray() throws IOException {
+  @Test
+  void testEmptyArray() throws IOException {
     JsonElement element = JsonParser.parseString("[]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
     reader.endArray();
   }
 
-  public void testNestedArrays() throws IOException {
+  @Test
+  void testNestedArrays() throws IOException {
     JsonElement element = JsonParser.parseString("[[],[[]]]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -172,7 +188,8 @@ public void testNestedArrays() throws IOException {
     reader.endArray();
   }
 
-  public void testNestedObjects() throws IOException {
+  @Test
+  void testNestedObjects() throws IOException {
     JsonElement element = JsonParser.parseString("{\"A\":{},\"B\":{\"C\":{}}}");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginObject();
@@ -188,14 +205,16 @@ public void testNestedObjects() throws IOException {
     reader.endObject();
   }
 
-  public void testEmptyObject() throws IOException {
+  @Test
+  void testEmptyObject() throws IOException {
     JsonElement element = JsonParser.parseString("{}");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginObject();
     reader.endObject();
   }
 
-  public void testSkipValue() throws IOException {
+  @Test
+  void testSkipValue() throws IOException {
     JsonElement element = JsonParser.parseString("[\"A\",{\"B\":[[]]},\"C\",[[]],\"D\",null]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -208,7 +227,8 @@ public void testSkipValue() throws IOException {
     reader.endArray();
   }
 
-  public void testWrongType() throws IOException {
+  @Test
+  void testWrongType() throws IOException {
     JsonElement element = JsonParser.parseString("[[],\"A\"]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
@@ -299,7 +319,8 @@ public void testWrongType() throws IOException {
     reader.endArray();
   }
 
-  public void testNextJsonElement() throws IOException {
+  @Test
+  void testNextJsonElement() throws IOException {
     final JsonElement element = JsonParser.parseString("{\"A\": 1, \"B\" : {}, \"C\" : []}");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginObject();
@@ -334,7 +355,8 @@ public void testNextJsonElement() throws IOException {
     }
   }
 
-  public void testEarlyClose() throws IOException {
+  @Test
+  void testEarlyClose() throws IOException {
     JsonElement element = JsonParser.parseString("[1, 2, 3]");
     JsonTreeReader reader = new JsonTreeReader(element);
     reader.beginArray();
diff --git a/gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java b/gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java
index f6a5bf33e8..a18824ba93 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java
@@ -15,22 +15,26 @@
  */
 package com.google.gson.internal.bind;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.JsonArray;
 import com.google.gson.JsonNull;
 import com.google.gson.JsonObject;
 import com.google.gson.stream.JsonToken;
 import java.io.IOException;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 @SuppressWarnings("resource")
-public class JsonTreeReaderTest extends TestCase {
-  public void testSkipValue_emptyJsonObject() throws IOException {
+class JsonTreeReaderTest {
+  @Test
+  void testSkipValue_emptyJsonObject() throws IOException {
     JsonTreeReader in = new JsonTreeReader(new JsonObject());
     in.skipValue();
     assertEquals(JsonToken.END_DOCUMENT, in.peek());
   }
 
-  public void testSkipValue_filledJsonObject() throws IOException {
+  @Test
+  void testSkipValue_filledJsonObject() throws IOException {
     JsonObject jsonObject = new JsonObject();
     JsonArray jsonArray = new JsonArray();
     jsonArray.add('c');
diff --git a/gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java b/gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java
index 094f04bd28..591e23a558 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java
@@ -16,13 +16,17 @@
 
 package com.google.gson.internal.bind;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import com.google.gson.JsonNull;
 import java.io.IOException;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 @SuppressWarnings("resource")
-public final class JsonTreeWriterTest extends TestCase {
-  public void testArray() throws IOException {
+class JsonTreeWriterTest {
+  @Test
+  void testArray() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.beginArray();
     writer.value(1);
@@ -32,7 +36,8 @@ public void testArray() throws IOException {
     assertEquals("[1,2,3]", writer.get().toString());
   }
 
-  public void testNestedArray() throws IOException {
+  @Test
+  void testNestedArray() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.beginArray();
     writer.beginArray();
@@ -45,7 +50,8 @@ public void testNestedArray() throws IOException {
     assertEquals("[[],[[]]]", writer.get().toString());
   }
 
-  public void testObject() throws IOException {
+  @Test
+  void testObject() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.beginObject();
     writer.name("A").value(1);
@@ -54,7 +60,8 @@ public void testObject() throws IOException {
     assertEquals("{\"A\":1,\"B\":2}", writer.get().toString());
   }
 
-  public void testNestedObject() throws IOException {
+  @Test
+  void testNestedObject() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.beginObject();
     writer.name("A");
@@ -70,7 +77,8 @@ public void testNestedObject() throws IOException {
     assertEquals("{\"A\":{\"B\":{}},\"C\":{}}", writer.get().toString());
   }
 
-  public void testWriteAfterClose() throws Exception {
+  @Test
+  void testWriteAfterClose() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setLenient(true);
     writer.beginArray();
@@ -84,7 +92,8 @@ public void testWriteAfterClose() throws Exception {
     }
   }
 
-  public void testPrematureClose() throws Exception {
+  @Test
+  void testPrematureClose() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setLenient(true);
     writer.beginArray();
@@ -95,7 +104,8 @@ public void testPrematureClose() throws Exception {
     }
   }
 
-  public void testSerializeNullsFalse() throws IOException {
+  @Test
+  void testSerializeNullsFalse() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setSerializeNulls(false);
     writer.beginObject();
@@ -105,7 +115,8 @@ public void testSerializeNullsFalse() throws IOException {
     assertEquals("{}", writer.get().toString());
   }
 
-  public void testSerializeNullsTrue() throws IOException {
+  @Test
+  void testSerializeNullsTrue() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setSerializeNulls(true);
     writer.beginObject();
@@ -115,40 +126,47 @@ public void testSerializeNullsTrue() throws IOException {
     assertEquals("{\"A\":null}", writer.get().toString());
   }
 
-  public void testEmptyWriter() {
+  @Test
+  void testEmptyWriter() {
     JsonTreeWriter writer = new JsonTreeWriter();
     assertEquals(JsonNull.INSTANCE, writer.get());
   }
 
-  public void testBeginArray() throws Exception {
+  @Test
+  void testBeginArray() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     assertEquals(writer, writer.beginArray());
   }
 
-  public void testBeginObject() throws Exception {
+  @Test
+  void testBeginObject() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     assertEquals(writer, writer.beginObject());
   }
 
-  public void testValueString() throws Exception {
+  @Test
+  void testValueString() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     String n = "as";
     assertEquals(writer, writer.value(n));
   }
 
-  public void testBoolValue() throws Exception {
+  @Test
+  void testBoolValue() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     boolean bool = true;
     assertEquals(writer, writer.value(bool));
   }
 
-  public void testBoolMaisValue() throws Exception {
+  @Test
+  void testBoolMaisValue() throws Exception {
     JsonTreeWriter writer = new JsonTreeWriter();
     Boolean bool = true;
     assertEquals(writer, writer.value(bool));
   }
 
-  public void testLenientNansAndInfinities() throws IOException {
+  @Test
+  void testLenientNansAndInfinities() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setLenient(true);
     writer.beginArray();
@@ -159,7 +177,8 @@ public void testLenientNansAndInfinities() throws IOException {
     assertEquals("[NaN,-Infinity,Infinity]", writer.get().toString());
   }
 
-  public void testStrictNansAndInfinities() throws IOException {
+  @Test
+  void testStrictNansAndInfinities() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setLenient(false);
     writer.beginArray();
@@ -180,7 +199,8 @@ public void testStrictNansAndInfinities() throws IOException {
     }
   }
 
-  public void testStrictBoxedNansAndInfinities() throws IOException {
+  @Test
+  void testStrictBoxedNansAndInfinities() throws IOException {
     JsonTreeWriter writer = new JsonTreeWriter();
     writer.setLenient(false);
     writer.beginArray();
diff --git a/gson/src/test/java/com/google/gson/internal/bind/RecursiveTypesResolveTest.java b/gson/src/test/java/com/google/gson/internal/bind/RecursiveTypesResolveTest.java
index a2bece26e1..c585cd921e 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/RecursiveTypesResolveTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/RecursiveTypesResolveTest.java
@@ -16,13 +16,13 @@
 
 package com.google.gson.internal.bind;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
 import com.google.gson.Gson;
 import com.google.gson.TypeAdapter;
 import com.google.gson.internal.$Gson$Types;
-import junit.framework.TestCase;
-
-import java.io.PrintStream;
-import java.lang.ref.WeakReference;
+import org.junit.jupiter.api.Test;
 
 /**
  * Test fixes for infinite recursion on {@link $Gson$Types#resolve(java.lang.reflect.Type, Class,
@@ -32,7 +32,7 @@
  * These tests originally caused {@link StackOverflowError} because of infinite recursion on attempts to
  * resolve generics on types, with an intermediate types like 'Foo2&lt;? extends ? super ? extends ... ? extends A&gt;'
  */
-public class RecursiveTypesResolveTest extends TestCase {
+class RecursiveTypesResolveTest {
 
   @SuppressWarnings("unused")
   private static class Foo1<A> {
@@ -46,38 +46,42 @@ private static class Foo2<B> {
   /**
    * Test simplest case of recursion.
    */
-
-  public void testRecursiveResolveSimple() {
+  @Test
+  void testRecursiveResolveSimple() {
     @SuppressWarnings("rawtypes")
     TypeAdapter<Foo1> adapter = new Gson().getAdapter(Foo1.class);
     assertNotNull(adapter);
   }
 
-  /**
+  /*
    * Tests belows check the behaviour of the methods changed for the fix.
    */
 
-  public void testDoubleSupertype() {
+  @Test
+  void testDoubleSupertype() {
     assertEquals($Gson$Types.supertypeOf(Number.class),
             $Gson$Types.supertypeOf($Gson$Types.supertypeOf(Number.class)));
   }
 
-  public void testDoubleSubtype() {
+  @Test
+  void testDoubleSubtype() {
     assertEquals($Gson$Types.subtypeOf(Number.class),
             $Gson$Types.subtypeOf($Gson$Types.subtypeOf(Number.class)));
   }
 
-  public void testSuperSubtype() {
+  @Test
+  void testSuperSubtype() {
     assertEquals($Gson$Types.subtypeOf(Object.class),
             $Gson$Types.supertypeOf($Gson$Types.subtypeOf(Number.class)));
   }
 
-  public void testSubSupertype() {
+  @Test
+  void testSubSupertype() {
     assertEquals($Gson$Types.subtypeOf(Object.class),
             $Gson$Types.subtypeOf($Gson$Types.supertypeOf(Number.class)));
   }
 
-  /**
+  /*
    * Tests for recursion while resolving type variables.
    */
 
@@ -91,13 +95,15 @@ private static class TestType2<X, Y> {
     TestType2<? super Y, ? super X> superReversedType;
   }
 
-  public void testRecursiveTypeVariablesResolve1() throws Exception {
+  @Test
+  void testRecursiveTypeVariablesResolve1() throws Exception {
     @SuppressWarnings("rawtypes")
     TypeAdapter<TestType> adapter = new Gson().getAdapter(TestType.class);
     assertNotNull(adapter);
   }
 
-  public void testRecursiveTypeVariablesResolve12() throws Exception {
+  @Test
+  void testRecursiveTypeVariablesResolve12() throws Exception {
     @SuppressWarnings("rawtypes")
     TypeAdapter<TestType2> adapter = new Gson().getAdapter(TestType2.class);
     assertNotNull(adapter);
diff --git a/gson/src/test/java/com/google/gson/internal/bind/util/ISO8601UtilsTest.java b/gson/src/test/java/com/google/gson/internal/bind/util/ISO8601UtilsTest.java
index bc0c9ec0f6..1e6083b147 100644
--- a/gson/src/test/java/com/google/gson/internal/bind/util/ISO8601UtilsTest.java
+++ b/gson/src/test/java/com/google/gson/internal/bind/util/ISO8601UtilsTest.java
@@ -1,15 +1,19 @@
 package com.google.gson.internal.bind.util;
 
-import org.junit.Test;
-import org.junit.function.ThrowingRunnable;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
 import java.text.ParseException;
 import java.text.ParsePosition;
-import java.util.*;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertThrows;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+import java.util.Locale;
+import java.util.TimeZone;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
 
-public class ISO8601UtilsTest {
+class ISO8601UtilsTest {
 
     private static TimeZone utcTimeZone() {
         return TimeZone.getTimeZone("UTC");
@@ -24,7 +28,7 @@ private static GregorianCalendar createUtcCalendar() {
     }
 
     @Test
-    public void testDateFormatString() {
+    void testDateFormatString() {
         GregorianCalendar calendar = new GregorianCalendar(utcTimeZone(), Locale.US);
         // Calendar was created with current time, must clear it
         calendar.clear();
@@ -36,7 +40,7 @@ public void testDateFormatString() {
     }
 
     @Test
-    public void testDateFormatWithMilliseconds() {
+    void testDateFormatWithMilliseconds() {
         long time = 1530209176870L;
         Date date = new Date(time);
         String dateStr = ISO8601Utils.format(date, true);
@@ -45,7 +49,7 @@ public void testDateFormatWithMilliseconds() {
     }
 
     @Test
-    public void testDateFormatWithTimezone() {
+    void testDateFormatWithTimezone() {
         long time = 1530209176870L;
         Date date = new Date(time);
         String dateStr = ISO8601Utils.format(date, true, TimeZone.getTimeZone("Brazil/East"));
@@ -54,7 +58,7 @@ public void testDateFormatWithTimezone() {
     }
 
     @Test
-    public void testDateParseWithDefaultTimezone() throws ParseException {
+    void testDateParseWithDefaultTimezone() throws ParseException {
         String dateStr = "2018-06-25";
         Date date = ISO8601Utils.parse(dateStr, new ParsePosition(0));
         Date expectedDate = new GregorianCalendar(2018, Calendar.JUNE, 25).getTime();
@@ -62,7 +66,7 @@ public void testDateParseWithDefaultTimezone() throws ParseException {
     }
 
     @Test
-    public void testDateParseWithTimezone() throws ParseException {
+    void testDateParseWithTimezone() throws ParseException {
         String dateStr = "2018-06-25T00:00:00-03:00";
         Date date = ISO8601Utils.parse(dateStr, new ParsePosition(0));
         GregorianCalendar calendar = createUtcCalendar();
@@ -72,7 +76,7 @@ public void testDateParseWithTimezone() throws ParseException {
     }
 
     @Test
-    public void testDateParseSpecialTimezone() throws ParseException {
+    void testDateParseSpecialTimezone() throws ParseException {
         String dateStr = "2018-06-25T00:02:00-02:58";
         Date date = ISO8601Utils.parse(dateStr, new ParsePosition(0));
         GregorianCalendar calendar = createUtcCalendar();
@@ -82,11 +86,11 @@ public void testDateParseSpecialTimezone() throws ParseException {
     }
 
     @Test
-    public void testDateParseInvalidTime() throws ParseException {
+    void testDateParseInvalidTime() throws ParseException {
         final String dateStr = "2018-06-25T61:60:62-03:00";
-        assertThrows(ParseException.class, new ThrowingRunnable() {
+        assertThrows(ParseException.class, new Executable() {
           @Override
-          public void run() throws Throwable {
+          public void execute() throws Throwable {
             ISO8601Utils.parse(dateStr, new ParsePosition(0));
           }
         });
diff --git a/gson/src/test/java/com/google/gson/internal/sql/SqlTypesGsonTest.java b/gson/src/test/java/com/google/gson/internal/sql/SqlTypesGsonTest.java
index 03e2185541..2eadf4e45e 100644
--- a/gson/src/test/java/com/google/gson/internal/sql/SqlTypesGsonTest.java
+++ b/gson/src/test/java/com/google/gson/internal/sql/SqlTypesGsonTest.java
@@ -1,26 +1,27 @@
 package com.google.gson.internal.sql;
 
-import java.sql.Date;
-import java.sql.Time;
-import java.sql.Timestamp;
-import java.util.Locale;
-import java.util.TimeZone;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.functional.DefaultTypeAdaptersTest;
 import com.google.gson.internal.JavaVersion;
+import java.sql.Date;
+import java.sql.Time;
+import java.sql.Timestamp;
+import java.util.Locale;
+import java.util.TimeZone;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public class SqlTypesGsonTest extends TestCase {
+class SqlTypesGsonTest {
   private Gson gson;
   private TimeZone oldTimeZone;
   private Locale oldLocale;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     this.oldTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));
     this.oldLocale = Locale.getDefault();
@@ -28,14 +29,14 @@ protected void setUp() throws Exception {
     gson = new Gson();
   }
 
-  @Override
-  protected void tearDown() throws Exception {
-    super.tearDown();
+  @AfterEach
+  void tearDown() throws Exception {
     TimeZone.setDefault(oldTimeZone);
     Locale.setDefault(oldLocale);
   }
 
-  public void testNullSerializationAndDeserialization() {
+  @Test
+  void testNullSerializationAndDeserialization() {
     testNullSerializationAndDeserialization(Date.class);
     testNullSerializationAndDeserialization(Time.class);
     testNullSerializationAndDeserialization(Timestamp.class);
@@ -45,20 +46,23 @@ private void testNullSerializationAndDeserialization(Class<?> c) {
     DefaultTypeAdaptersTest.testNullSerializationAndDeserialization(gson, c);
   }
 
-  public void testDefaultSqlDateSerialization() {
+  @Test
+  void testDefaultSqlDateSerialization() {
     java.sql.Date instant = new java.sql.Date(1259875082000L);
     String json = gson.toJson(instant);
     assertEquals("\"Dec 3, 2009\"", json);
   }
 
-  public void testDefaultSqlDateDeserialization() {
+  @Test
+  void testDefaultSqlDateDeserialization() {
     String json = "'Dec 3, 2009'";
     java.sql.Date extracted = gson.fromJson(json, java.sql.Date.class);
     DefaultTypeAdaptersTest.assertEqualsDate(extracted, 2009, 11, 3);
   }
 
   // http://code.google.com/p/google-gson/issues/detail?id=230
-  public void testSqlDateSerialization() throws Exception {
+  @Test
+  void testSqlDateSerialization() throws Exception {
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
     Locale defaultLocale = Locale.getDefault();
@@ -75,19 +79,22 @@ public void testSqlDateSerialization() throws Exception {
     }
   }
 
-  public void testDefaultSqlTimeSerialization() {
+  @Test
+  void testDefaultSqlTimeSerialization() {
     Time now = new Time(1259875082000L);
     String json = gson.toJson(now);
     assertEquals("\"01:18:02 PM\"", json);
   }
 
-  public void testDefaultSqlTimeDeserialization() {
+  @Test
+  void testDefaultSqlTimeDeserialization() {
     String json = "'1:18:02 PM'";
     Time extracted = gson.fromJson(json, Time.class);
     DefaultTypeAdaptersTest.assertEqualsTime(extracted, 13, 18, 2);
   }
 
-  public void testDefaultSqlTimestampSerialization() {
+  @Test
+  void testDefaultSqlTimestampSerialization() {
     Timestamp now = new java.sql.Timestamp(1259875082000L);
     String json = gson.toJson(now);
     if (JavaVersion.isJava9OrLater()) {
@@ -97,7 +104,8 @@ public void testDefaultSqlTimestampSerialization() {
     }
   }
 
-  public void testDefaultSqlTimestampDeserialization() {
+  @Test
+  void testDefaultSqlTimestampDeserialization() {
     String json = "'Dec 3, 2009 1:18:02 PM'";
     Timestamp extracted = gson.fromJson(json, Timestamp.class);
     DefaultTypeAdaptersTest.assertEqualsDate(extracted, 2009, 11, 3);
@@ -105,7 +113,8 @@ public void testDefaultSqlTimestampDeserialization() {
   }
 
   // http://code.google.com/p/google-gson/issues/detail?id=230
-  public void testTimestampSerialization() throws Exception {
+  @Test
+  void testTimestampSerialization() throws Exception {
     TimeZone defaultTimeZone = TimeZone.getDefault();
     TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
     Locale defaultLocale = Locale.getDefault();
diff --git a/gson/src/test/java/com/google/gson/internal/sql/SqlTypesSupportTest.java b/gson/src/test/java/com/google/gson/internal/sql/SqlTypesSupportTest.java
index ea496f4ac9..8a8e1fc6f3 100644
--- a/gson/src/test/java/com/google/gson/internal/sql/SqlTypesSupportTest.java
+++ b/gson/src/test/java/com/google/gson/internal/sql/SqlTypesSupportTest.java
@@ -1,9 +1,13 @@
 package com.google.gson.internal.sql;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
-public class SqlTypesSupportTest extends TestCase {
-  public void testSupported() {
+import org.junit.jupiter.api.Test;
+
+class SqlTypesSupportTest {
+  @Test
+  void testSupported() {
     assertTrue(SqlTypesSupport.SUPPORTS_SQL_TYPES);
 
     assertNotNull(SqlTypesSupport.DATE_DATE_TYPE);
diff --git a/gson/src/test/java/com/google/gson/metrics/PerformanceTest.java b/gson/src/test/java/com/google/gson/metrics/PerformanceTest.java
index d05cf4be18..4f16543eeb 100644
--- a/gson/src/test/java/com/google/gson/metrics/PerformanceTest.java
+++ b/gson/src/test/java/com/google/gson/metrics/PerformanceTest.java
@@ -16,45 +16,46 @@
 
 package com.google.gson.metrics;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.JsonParseException;
 import com.google.gson.annotations.Expose;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.io.StringWriter;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
 
 /**
- * Tests to measure performance for Gson. All tests in this file will be disabled in code. To run
- * them remove disabled_ prefix from the tests and run them.
- * 
+ * Tests to measure performance of Gson. All tests in this class are disabled. To run
+ * them remove {@code @Disabled} from this class and the test method.
+ *
  * @author Inderjeet Singh
  * @author Joel Leitch
  */
-public class PerformanceTest extends TestCase {
+@Disabled("Only for manual testing")
+class PerformanceTest {
   private static final int COLLECTION_SIZE = 5000;
 
   private static final int NUM_ITERATIONS = 100;
 
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new Gson();
   }
-  
-  public void testDummy() {
-    // This is here to prevent Junit for complaining when we disable all tests.
-  }
 
-  public void disabled_testStringDeserialization() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testStringDeserialization() {
     StringBuilder sb = new StringBuilder(8096);
     sb.append("Error Yippie");
 
@@ -70,7 +71,7 @@ public void disabled_testStringDeserialization() {
       }
     }
   }
-  
+
   private void parseLongJson(String json) throws JsonParseException {
     ExceptionHolder target = gson.fromJson(json, ExceptionHolder.class);
     assertTrue(target.message.contains("Error"));
@@ -80,13 +81,13 @@ private void parseLongJson(String json) throws JsonParseException {
   private static class ExceptionHolder {
     public final String message;
     public final String stackTrace;
-    
+
     // For use by Gson
     @SuppressWarnings("unused")
     private ExceptionHolder() {
       this("", "");
     }
-    public ExceptionHolder(String message, String stackTrace) {
+    ExceptionHolder(String message, String stackTrace) {
       this.message = message;
       this.stackTrace = stackTrace;
     }
@@ -107,23 +108,27 @@ private CollectionEntry() {
       this.value = value;
     }
   }
-  
+
   /**
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=96
    */
-  public void disabled_testLargeCollectionSerialization() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testLargeCollectionSerialization() {
     int count = 1400000;
     List<CollectionEntry> list = new ArrayList<CollectionEntry>(count);
     for (int i = 0; i < count; ++i) {
       list.add(new CollectionEntry("name"+i,"value"+i));
-    }    
+    }
     gson.toJson(list);
   }
-  
+
   /**
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=96
    */
-  public void disabled_testLargeCollectionDeserialization() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testLargeCollectionDeserialization() {
     StringBuilder sb = new StringBuilder();
     int count = 87000;
     boolean first = true;
@@ -135,7 +140,7 @@ public void disabled_testLargeCollectionDeserialization() {
         sb.append(',');
       }
       sb.append("{name:'name").append(i).append("',value:'value").append(i).append("'}");
-    }    
+    }
     sb.append(']');
     String json = sb.toString();
     Type collectionType = new TypeToken<ArrayList<CollectionEntry>>(){}.getType();
@@ -147,7 +152,9 @@ public void disabled_testLargeCollectionDeserialization() {
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=96
    */
   // Last I tested, Gson was able to serialize upto 14MB byte array
-  public void disabled_testByteArraySerialization() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testByteArraySerialization() {
     for (int size = 4145152; true; size += 1036288) {
       byte[] ba = new byte[size];
       for (int i = 0; i < size; ++i) {
@@ -157,12 +164,14 @@ public void disabled_testByteArraySerialization() {
       System.out.printf("Gson could serialize a byte array of size: %d\n", size);
     }
   }
-  
+
   /**
    * Created in response to http://code.google.com/p/google-gson/issues/detail?id=96
    */
   // Last I tested, Gson was able to deserialize a byte array of 11MB
-  public void disable_testByteArrayDeserialization() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testByteArrayDeserialization() {
     for (int numElements = 10639296; true; numElements += 16384) {
       StringBuilder sb = new StringBuilder(numElements*2);
       sb.append("[");
@@ -185,86 +194,98 @@ public void disable_testByteArrayDeserialization() {
 // The tests to measure serialization and deserialization performance of Gson
 // Based on the discussion at
 // http://groups.google.com/group/google-gson/browse_thread/thread/7a50b17a390dfaeb
-// Test results: 10/19/2009 
+// Test results: 10/19/2009
 // Serialize classes avg time: 60 ms
 // Deserialized classes avg time: 70 ms
 // Serialize exposed classes avg time: 159 ms
 // Deserialized exposed classes avg time: 173 ms
-  
-  public void disabled_testSerializeClasses() {
-    ClassWithList c = new ClassWithList("str"); 
-    for (int i = 0; i < COLLECTION_SIZE; ++i) { 
-      c.list.add(new ClassWithField("element-" + i)); 
+
+  @Disabled("Only for manual testing")
+  @Test
+  void testSerializeClasses() {
+    ClassWithList c = new ClassWithList("str");
+    for (int i = 0; i < COLLECTION_SIZE; ++i) {
+      c.list.add(new ClassWithField("element-" + i));
+    }
+    StringWriter w = new StringWriter();
+    long t1 = System.currentTimeMillis();
+    for (int i = 0; i < NUM_ITERATIONS; ++i) {
+      gson.toJson(c, w);
     }
-    StringWriter w = new StringWriter(); 
-    long t1 = System.currentTimeMillis(); 
-    for (int i = 0; i < NUM_ITERATIONS; ++i) { 
-      gson.toJson(c, w); 
-    } 
-    long t2 = System.currentTimeMillis(); 
+    long t2 = System.currentTimeMillis();
     long avg = (t2 - t1) / NUM_ITERATIONS;
     System.out.printf("Serialize classes avg time: %d ms\n", avg);
   }
 
-  public void disabled_testDeserializeClasses() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testDeserializeClasses() {
     String json = buildJsonForClassWithList();
     ClassWithList[] target = new ClassWithList[NUM_ITERATIONS];
-    long t1 = System.currentTimeMillis(); 
+    long t1 = System.currentTimeMillis();
     for (int i = 0; i < NUM_ITERATIONS; ++i) {
       target[i] = gson.fromJson(json, ClassWithList.class);
     }
-    long t2 = System.currentTimeMillis(); 
+    long t2 = System.currentTimeMillis();
     long avg = (t2 - t1) / NUM_ITERATIONS;
     System.out.printf("Deserialize classes avg time: %d ms\n", avg);
   }
-  
-  public void disable_testLargeObjectSerializationAndDeserialization() {
+
+  @Disabled("Only for manual testing")
+  @Test
+  void testLargeObjectSerializationAndDeserialization() {
     Map<String, Long> largeObject = new HashMap<String, Long>();
     for (long l = 0; l < 100000; l++) {
       largeObject.put("field" + l, l);
     }
-    
-    long t1 = System.currentTimeMillis(); 
+
+    long t1 = System.currentTimeMillis();
     String json = gson.toJson(largeObject);
     long t2 = System.currentTimeMillis();
     System.out.printf("Large object serialized in: %d ms\n", (t2 - t1));
 
-    t1 = System.currentTimeMillis(); 
+    t1 = System.currentTimeMillis();
     gson.fromJson(json, new TypeToken<Map<String, Long>>() {}.getType());
     t2 = System.currentTimeMillis();
     System.out.printf("Large object deserialized in: %d ms\n", (t2 - t1));
-    
+
   }
 
-  public void disabled_testSerializeExposedClasses() {
-    ClassWithListOfObjects c1 = new ClassWithListOfObjects("str"); 
-    for (int i1 = 0; i1 < COLLECTION_SIZE; ++i1) { 
-      c1.list.add(new ClassWithExposedField("element-" + i1)); 
+  @Disabled("Only for manual testing")
+  @Test
+  void testSerializeExposedClasses() {
+    ClassWithListOfObjects c1 = new ClassWithListOfObjects("str");
+    for (int i1 = 0; i1 < COLLECTION_SIZE; ++i1) {
+      c1.list.add(new ClassWithExposedField("element-" + i1));
     }
-    ClassWithListOfObjects c = c1; 
-    StringWriter w = new StringWriter(); 
-    long t1 = System.currentTimeMillis(); 
-    for (int i = 0; i < NUM_ITERATIONS; ++i) { 
-      gson.toJson(c, w); 
-    } 
-    long t2 = System.currentTimeMillis(); 
+    ClassWithListOfObjects c = c1;
+    StringWriter w = new StringWriter();
+    long t1 = System.currentTimeMillis();
+    for (int i = 0; i < NUM_ITERATIONS; ++i) {
+      gson.toJson(c, w);
+    }
+    long t2 = System.currentTimeMillis();
     long avg = (t2 - t1) / NUM_ITERATIONS;
     System.out.printf("Serialize exposed classes avg time: %d ms\n", avg);
   }
 
-  public void disabled_testDeserializeExposedClasses() {
+  @Disabled("Only for manual testing")
+  @Test
+  void testDeserializeExposedClasses() {
     String json = buildJsonForClassWithList();
     ClassWithListOfObjects[] target = new ClassWithListOfObjects[NUM_ITERATIONS];
-    long t1 = System.currentTimeMillis(); 
+    long t1 = System.currentTimeMillis();
     for (int i = 0; i < NUM_ITERATIONS; ++i) {
       target[i] = gson.fromJson(json, ClassWithListOfObjects.class);
     }
-    long t2 = System.currentTimeMillis(); 
+    long t2 = System.currentTimeMillis();
     long avg = (t2 - t1) / NUM_ITERATIONS;
     System.out.printf("Deserialize exposed classes avg time: %d ms\n", avg);
   }
 
-  public void disabled_testLargeGsonMapRoundTrip() throws Exception {
+  @Disabled("Only for manual testing")
+  @Test
+  void testLargeGsonMapRoundTrip() throws Exception {
     Map<Long, Long> original = new HashMap<Long, Long>();
     for (long i = 0; i < 1000000; i++) {
       original.put(i, i + 1);
@@ -296,8 +317,8 @@ private String buildJsonForClassWithList() {
   }
 
   @SuppressWarnings("unused")
-  private static final class ClassWithList { 
-    final String field; 
+  private static final class ClassWithList {
+    final String field;
     final List<ClassWithField> list = new ArrayList<ClassWithField>(COLLECTION_SIZE);
     ClassWithList() {
       this(null);
@@ -305,24 +326,24 @@ private static final class ClassWithList {
     ClassWithList(String field) {
       this.field = field;
     }
-  } 
+  }
 
   @SuppressWarnings("unused")
-  private static final class ClassWithField { 
+  private static final class ClassWithField {
     final String field;
     ClassWithField() {
       this("");
     }
-    public ClassWithField(String field) { 
-      this.field = field; 
-    } 
+    public ClassWithField(String field) {
+      this.field = field;
+    }
   }
 
   @SuppressWarnings("unused")
-  private static final class ClassWithListOfObjects { 
-    @Expose 
-    final String field; 
-    @Expose 
+  private static final class ClassWithListOfObjects {
+    @Expose
+    final String field;
+    @Expose
     final List<ClassWithExposedField> list = new ArrayList<ClassWithExposedField>(COLLECTION_SIZE);
     ClassWithListOfObjects() {
       this(null);
@@ -330,17 +351,17 @@ private static final class ClassWithListOfObjects {
     ClassWithListOfObjects(String field) {
       this.field = field;
     }
-  } 
+  }
 
   @SuppressWarnings("unused")
-  private static final class ClassWithExposedField { 
-    @Expose 
+  private static final class ClassWithExposedField {
+    @Expose
     final String field;
     ClassWithExposedField() {
       this("");
     }
-    ClassWithExposedField(String field) { 
-      this.field = field; 
-    } 
+    ClassWithExposedField(String field) {
+      this.field = field;
+    }
   }
 }
\ No newline at end of file
diff --git a/gson/src/test/java/com/google/gson/reflect/TypeTokenTest.java b/gson/src/test/java/com/google/gson/reflect/TypeTokenTest.java
index 40572716bf..f154c5546c 100644
--- a/gson/src/test/java/com/google/gson/reflect/TypeTokenTest.java
+++ b/gson/src/test/java/com/google/gson/reflect/TypeTokenTest.java
@@ -16,19 +16,23 @@
 
 package com.google.gson.reflect;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.RandomAccess;
 import java.util.Set;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.Test;
 
 /**
  * @author Jesse Wilson
  */
 @SuppressWarnings({"deprecation"})
-public final class TypeTokenTest extends TestCase {
+class TypeTokenTest {
 
   List<Integer> listOfInteger = null;
   List<Number> listOfNumber = null;
@@ -37,14 +41,16 @@ public final class TypeTokenTest extends TestCase {
   List<Set<String>> listOfSetOfString = null;
   List<Set<?>> listOfSetOfUnknown = null;
 
-  public void testIsAssignableFromRawTypes() {
+  @Test
+  void testIsAssignableFromRawTypes() {
     assertTrue(TypeToken.get(Object.class).isAssignableFrom(String.class));
     assertFalse(TypeToken.get(String.class).isAssignableFrom(Object.class));
     assertTrue(TypeToken.get(RandomAccess.class).isAssignableFrom(ArrayList.class));
     assertFalse(TypeToken.get(ArrayList.class).isAssignableFrom(RandomAccess.class));
   }
 
-  public void testIsAssignableFromWithTypeParameters() throws Exception {
+  @Test
+  void testIsAssignableFromWithTypeParameters() throws Exception {
     Type a = getClass().getDeclaredField("listOfInteger").getGenericType();
     Type b = getClass().getDeclaredField("listOfNumber").getGenericType();
     assertTrue(TypeToken.get(a).isAssignableFrom(a));
@@ -56,7 +62,8 @@ public void testIsAssignableFromWithTypeParameters() throws Exception {
     assertFalse(TypeToken.get(b).isAssignableFrom(a));
   }
 
-  public void testIsAssignableFromWithBasicWildcards() throws Exception {
+  @Test
+  void testIsAssignableFromWithBasicWildcards() throws Exception {
     Type a = getClass().getDeclaredField("listOfString").getGenericType();
     Type b = getClass().getDeclaredField("listOfUnknown").getGenericType();
     assertTrue(TypeToken.get(a).isAssignableFrom(a));
@@ -69,7 +76,8 @@ public void testIsAssignableFromWithBasicWildcards() throws Exception {
     // assertTrue(TypeToken.get(b).isAssignableFrom(a));
   }
 
-  public void testIsAssignableFromWithNestedWildcards() throws Exception {
+  @Test
+  void testIsAssignableFromWithNestedWildcards() throws Exception {
     Type a = getClass().getDeclaredField("listOfSetOfString").getGenericType();
     Type b = getClass().getDeclaredField("listOfSetOfUnknown").getGenericType();
     assertTrue(TypeToken.get(a).isAssignableFrom(a));
@@ -81,7 +89,8 @@ public void testIsAssignableFromWithNestedWildcards() throws Exception {
     assertFalse(TypeToken.get(b).isAssignableFrom(a));
   }
 
-  public void testArrayFactory() {
+  @Test
+  void testArrayFactory() {
     TypeToken<?> expectedStringArray = new TypeToken<String[]>() {};
     assertEquals(expectedStringArray, TypeToken.getArray(String.class));
 
@@ -90,7 +99,8 @@ public void testArrayFactory() {
     assertEquals(expectedListOfStringArray, TypeToken.getArray(listOfString));
   }
 
-  public void testParameterizedFactory() {
+  @Test
+  void testParameterizedFactory() {
     TypeToken<?> expectedListOfString = new TypeToken<List<String>>() {};
     assertEquals(expectedListOfString, TypeToken.getParameterized(List.class, String.class));
 
diff --git a/gson/src/test/java/com/google/gson/regression/JsonAdapterNullSafeTest.java b/gson/src/test/java/com/google/gson/regression/JsonAdapterNullSafeTest.java
index a197243f15..b4628f2ef0 100644
--- a/gson/src/test/java/com/google/gson/regression/JsonAdapterNullSafeTest.java
+++ b/gson/src/test/java/com/google/gson/regression/JsonAdapterNullSafeTest.java
@@ -15,23 +15,26 @@
  */
 package com.google.gson.regression;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.Gson;
 import com.google.gson.TypeAdapter;
 import com.google.gson.TypeAdapterFactory;
 import com.google.gson.annotations.JsonAdapter;
 import com.google.gson.reflect.TypeToken;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public class JsonAdapterNullSafeTest extends TestCase {
+class JsonAdapterNullSafeTest {
   private final Gson gson = new Gson();
 
-  public void testNullSafeBugSerialize() throws Exception {
+  @Test
+  void testNullSafeBugSerialize() throws Exception {
     Device device = new Device("ec57803e");
     gson.toJson(device);
   }
 
-  public void testNullSafeBugDeserialize() throws Exception {
+  @Test
+  void testNullSafeBugDeserialize() throws Exception {
     Device device = gson.fromJson("{'id':'ec57803e2'}", Device.class);
     assertEquals("ec57803e2", device.id);
   }
diff --git a/gson/src/test/java/com/google/gson/regression/OSGiTest.java b/gson/src/test/java/com/google/gson/regression/OSGiTest.java
index 64a7e371ab..742c201bfe 100644
--- a/gson/src/test/java/com/google/gson/regression/OSGiTest.java
+++ b/gson/src/test/java/com/google/gson/regression/OSGiTest.java
@@ -15,25 +15,29 @@
  */
 package com.google.gson.regression;
 
-import java.io.InputStream;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.jar.Manifest;
+import org.junit.jupiter.api.Test;
 
-import junit.framework.TestCase;
-
-public class OSGiTest extends TestCase {
-    public void testComGoogleGsonAnnotationsPackage() throws Exception {
+class OSGiTest {
+    @Test
+    void testComGoogleGsonAnnotationsPackage() throws Exception {
         Manifest mf = findManifest("com.google.gson");
         String importPkg = mf.getMainAttributes().getValue("Import-Package");
         assertNotNull("Import-Package statement is there", importPkg);
         assertSubstring("There should be com.google.gson.annotations dependency", importPkg, "com.google.gson.annotations");
     }
 
-    public void testSunMiscImportPackage() throws Exception {
+    @Test
+    void testSunMiscImportPackage() throws Exception {
         Manifest mf = findManifest("com.google.gson");
         String importPkg = mf.getMainAttributes().getValue("Import-Package");
         assertNotNull("Import-Package statement is there", importPkg);
diff --git a/gson/src/test/java/com/google/gson/stream/JsonReaderPathTest.java b/gson/src/test/java/com/google/gson/stream/JsonReaderPathTest.java
index ab802be1d7..f18d1ba8f0 100644
--- a/gson/src/test/java/com/google/gson/stream/JsonReaderPathTest.java
+++ b/gson/src/test/java/com/google/gson/stream/JsonReaderPathTest.java
@@ -16,35 +16,22 @@
 
 package com.google.gson.stream;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import com.google.gson.JsonElement;
 import com.google.gson.internal.Streams;
 import com.google.gson.internal.bind.JsonTreeReader;
 import java.io.IOException;
 import java.io.StringReader;
-import java.util.Arrays;
-import java.util.List;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-import org.junit.runners.Parameterized;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assume.assumeTrue;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
 
 @SuppressWarnings("resource")
-@RunWith(Parameterized.class)
-public class JsonReaderPathTest {
-  @Parameterized.Parameters(name = "{0}")
-  public static List<Object[]> parameters() {
-    return Arrays.asList(
-        new Object[] { Factory.STRING_READER },
-        new Object[] { Factory.OBJECT_READER }
-    );
-  }
-
-  @Parameterized.Parameter
-  public Factory factory;
-
-  @Test public void path() throws IOException {
+class JsonReaderPathTest {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void path(Factory factory) throws IOException {
     JsonReader reader = factory.create("{\"a\":[2,true,false,null,\"b\",{\"c\":\"d\"},[3]]}");
     assertEquals("$", reader.getPreviousPath());
     assertEquals("$", reader.getPath());
@@ -101,7 +88,9 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  @Test public void objectPath() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void objectPath(Factory factory) throws IOException {
     JsonReader reader = factory.create("{\"a\":1,\"b\":2}");
     assertEquals("$", reader.getPreviousPath());
     assertEquals("$", reader.getPath());
@@ -156,7 +145,9 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  @Test public void arrayPath() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void arrayPath(Factory factory) throws IOException {
     JsonReader reader = factory.create("[1,2]");
     assertEquals("$", reader.getPreviousPath());
     assertEquals("$", reader.getPath());
@@ -197,9 +188,9 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  @Test public void multipleTopLevelValuesInOneDocument() throws IOException {
-    assumeTrue(factory == Factory.STRING_READER);
-
+  @Test
+  void multipleTopLevelValuesInOneDocument() throws IOException {
+    Factory factory = Factory.STRING_READER;
     JsonReader reader = factory.create("[][]");
     reader.setLenient(true);
     reader.beginArray();
@@ -212,7 +203,9 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  @Test public void skipArrayElements() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void skipArrayElements(Factory factory) throws IOException {
     JsonReader reader = factory.create("[1,2,3]");
     reader.beginArray();
     reader.skipValue();
@@ -221,7 +214,9 @@ public static List<Object[]> parameters() {
     assertEquals("$[2]", reader.getPath());
   }
 
-  @Test public void skipObjectNames() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void skipObjectNames(Factory factory) throws IOException {
     JsonReader reader = factory.create("{\"a\":1}");
     reader.beginObject();
     reader.skipValue();
@@ -229,7 +224,9 @@ public static List<Object[]> parameters() {
     assertEquals("$.null", reader.getPath());
   }
 
-  @Test public void skipObjectValues() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void skipObjectValues(Factory factory) throws IOException {
     JsonReader reader = factory.create("{\"a\":1,\"b\":2}");
     reader.beginObject();
     assertEquals("$.", reader.getPreviousPath());
@@ -243,7 +240,9 @@ public static List<Object[]> parameters() {
     assertEquals("$.b", reader.getPath());
   }
 
-  @Test public void skipNestedStructures() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void skipNestedStructures(Factory factory) throws IOException {
     JsonReader reader = factory.create("[[1,2,3],4]");
     reader.beginArray();
     reader.skipValue();
@@ -251,7 +250,9 @@ public static List<Object[]> parameters() {
     assertEquals("$[1]", reader.getPath());
   }
 
-  @Test public void arrayOfObjects() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void arrayOfObjects(Factory factory) throws IOException {
     JsonReader reader = factory.create("[{},{},{}]");
     reader.beginArray();
     assertEquals("$[0]", reader.getPreviousPath());
@@ -279,7 +280,9 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  @Test public void arrayOfArrays() throws IOException {
+  @ParameterizedTest
+  @EnumSource(Factory.class)
+  void arrayOfArrays(Factory factory) throws IOException {
     JsonReader reader = factory.create("[[],[],[]]");
     reader.beginArray();
     assertEquals("$[0]", reader.getPreviousPath());
@@ -307,7 +310,7 @@ public static List<Object[]> parameters() {
     assertEquals("$", reader.getPath());
   }
 
-  public enum Factory {
+  enum Factory {
     STRING_READER {
       @Override public JsonReader create(String data) {
         return new JsonReader(new StringReader(data));
diff --git a/gson/src/test/java/com/google/gson/stream/JsonReaderTest.java b/gson/src/test/java/com/google/gson/stream/JsonReaderTest.java
index d305462479..0b0a2b85bd 100644
--- a/gson/src/test/java/com/google/gson/stream/JsonReaderTest.java
+++ b/gson/src/test/java/com/google/gson/stream/JsonReaderTest.java
@@ -16,13 +16,6 @@
 
 package com.google.gson.stream;
 
-import java.io.EOFException;
-import java.io.IOException;
-import java.io.Reader;
-import java.io.StringReader;
-import java.util.Arrays;
-import junit.framework.TestCase;
-
 import static com.google.gson.stream.JsonToken.BEGIN_ARRAY;
 import static com.google.gson.stream.JsonToken.BEGIN_OBJECT;
 import static com.google.gson.stream.JsonToken.BOOLEAN;
@@ -32,10 +25,23 @@
 import static com.google.gson.stream.JsonToken.NULL;
 import static com.google.gson.stream.JsonToken.NUMBER;
 import static com.google.gson.stream.JsonToken.STRING;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.io.Reader;
+import java.io.StringReader;
+import java.util.Arrays;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
 
 @SuppressWarnings("resource")
-public final class JsonReaderTest extends TestCase {
-  public void testReadArray() throws IOException {
+class JsonReaderTest {
+  @Test
+  void testReadArray() throws IOException {
     JsonReader reader = new JsonReader(reader("[true, true]"));
     reader.beginArray();
     assertEquals(true, reader.nextBoolean());
@@ -44,7 +50,8 @@ public void testReadArray() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testReadEmptyArray() throws IOException {
+  @Test
+  void testReadEmptyArray() throws IOException {
     JsonReader reader = new JsonReader(reader("[]"));
     reader.beginArray();
     assertFalse(reader.hasNext());
@@ -52,7 +59,8 @@ public void testReadEmptyArray() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testReadObject() throws IOException {
+  @Test
+  void testReadObject() throws IOException {
     JsonReader reader = new JsonReader(reader(
         "{\"a\": \"android\", \"b\": \"banana\"}"));
     reader.beginObject();
@@ -64,7 +72,8 @@ public void testReadObject() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testReadEmptyObject() throws IOException {
+  @Test
+  void testReadEmptyObject() throws IOException {
     JsonReader reader = new JsonReader(reader("{}"));
     reader.beginObject();
     assertFalse(reader.hasNext());
@@ -72,7 +81,8 @@ public void testReadEmptyObject() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipArray() throws IOException {
+  @Test
+  void testSkipArray() throws IOException {
     JsonReader reader = new JsonReader(reader(
         "{\"a\": [\"one\", \"two\", \"three\"], \"b\": 123}"));
     reader.beginObject();
@@ -84,7 +94,8 @@ public void testSkipArray() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipArrayAfterPeek() throws Exception {
+  @Test
+  void testSkipArrayAfterPeek() throws Exception {
     JsonReader reader = new JsonReader(reader(
         "{\"a\": [\"one\", \"two\", \"three\"], \"b\": 123}"));
     reader.beginObject();
@@ -97,14 +108,16 @@ public void testSkipArrayAfterPeek() throws Exception {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipTopLevelObject() throws Exception {
+  @Test
+  void testSkipTopLevelObject() throws Exception {
     JsonReader reader = new JsonReader(reader(
         "{\"a\": [\"one\", \"two\", \"three\"], \"b\": 123}"));
     reader.skipValue();
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipObject() throws IOException {
+  @Test
+  void testSkipObject() throws IOException {
     JsonReader reader = new JsonReader(reader(
         "{\"a\": { \"c\": [], \"d\": [true, true, {}] }, \"b\": \"banana\"}"));
     reader.beginObject();
@@ -116,7 +129,8 @@ public void testSkipObject() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipObjectAfterPeek() throws Exception {
+  @Test
+  void testSkipObjectAfterPeek() throws Exception {
     String json = "{" + "  \"one\": { \"num\": 1 }"
         + ", \"two\": { \"num\": 2 }" + ", \"three\": { \"num\": 3 }" + "}";
     JsonReader reader = new JsonReader(reader(json));
@@ -133,7 +147,8 @@ public void testSkipObjectAfterPeek() throws Exception {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipInteger() throws IOException {
+  @Test
+  void testSkipInteger() throws IOException {
     JsonReader reader = new JsonReader(reader(
         "{\"a\":123456789,\"b\":-123456789}"));
     reader.beginObject();
@@ -145,7 +160,8 @@ public void testSkipInteger() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipDouble() throws IOException {
+  @Test
+  void testSkipDouble() throws IOException {
     JsonReader reader = new JsonReader(reader(
         "{\"a\":-123.456e-789,\"b\":123456789.0}"));
     reader.beginObject();
@@ -157,7 +173,8 @@ public void testSkipDouble() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testHelloWorld() throws IOException {
+  @Test
+  void testHelloWorld() throws IOException {
     String json = "{\n" +
         "   \"hello\": true,\n" +
         "   \"foo\": [\"world\"]\n" +
@@ -174,7 +191,8 @@ public void testHelloWorld() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testInvalidJsonInput() throws IOException {
+  @Test
+  void testInvalidJsonInput() throws IOException {
     String json = "{\n"
         + "   \"h\\ello\": true,\n"
         + "   \"foo\": [\"world\"]\n"
@@ -188,9 +206,10 @@ public void testInvalidJsonInput() throws IOException {
     } catch (IOException expected) {
     }
   }
-  
+
   @SuppressWarnings("unused")
-  public void testNulls() {
+  @Test
+  void testNulls() {
     try {
       new JsonReader(null);
       fail();
@@ -198,7 +217,8 @@ public void testNulls() {
     }
   }
 
-  public void testEmptyString() {
+  @Test
+  void testEmptyString() {
     try {
       new JsonReader(reader("")).beginArray();
       fail();
@@ -211,7 +231,8 @@ public void testEmptyString() {
     }
   }
 
-  public void testCharacterUnescaping() throws IOException {
+  @Test
+  void testCharacterUnescaping() throws IOException {
     String json = "[\"a\","
         + "\"a\\\"\","
         + "\"\\\"\","
@@ -257,7 +278,8 @@ public void testCharacterUnescaping() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testUnescapingInvalidCharacters() throws IOException {
+  @Test
+  void testUnescapingInvalidCharacters() throws IOException {
     String json = "[\"\\u000g\"]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -268,7 +290,8 @@ public void testUnescapingInvalidCharacters() throws IOException {
     }
   }
 
-  public void testUnescapingTruncatedCharacters() throws IOException {
+  @Test
+  void testUnescapingTruncatedCharacters() throws IOException {
     String json = "[\"\\u000";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -279,7 +302,8 @@ public void testUnescapingTruncatedCharacters() throws IOException {
     }
   }
 
-  public void testUnescapingTruncatedSequence() throws IOException {
+  @Test
+  void testUnescapingTruncatedSequence() throws IOException {
     String json = "[\"\\";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -290,7 +314,8 @@ public void testUnescapingTruncatedSequence() throws IOException {
     }
   }
 
-  public void testIntegersWithFractionalPartSpecified() throws IOException {
+  @Test
+  void testIntegersWithFractionalPartSpecified() throws IOException {
     JsonReader reader = new JsonReader(reader("[1.0,1.0,1.0]"));
     reader.beginArray();
     assertEquals(1.0, reader.nextDouble());
@@ -298,7 +323,8 @@ public void testIntegersWithFractionalPartSpecified() throws IOException {
     assertEquals(1L, reader.nextLong());
   }
 
-  public void testDoubles() throws IOException {
+  @Test
+  void testDoubles() throws IOException {
     String json = "[-0.0,"
         + "1.0,"
         + "1.7976931348623157E308,"
@@ -323,7 +349,8 @@ public void testDoubles() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testStrictNonFiniteDoubles() throws IOException {
+  @Test
+  void testStrictNonFiniteDoubles() throws IOException {
     String json = "[NaN]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -334,7 +361,8 @@ public void testStrictNonFiniteDoubles() throws IOException {
     }
   }
 
-  public void testStrictQuotedNonFiniteDoubles() throws IOException {
+  @Test
+  void testStrictQuotedNonFiniteDoubles() throws IOException {
     String json = "[\"NaN\"]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -345,7 +373,8 @@ public void testStrictQuotedNonFiniteDoubles() throws IOException {
     }
   }
 
-  public void testLenientNonFiniteDoubles() throws IOException {
+  @Test
+  void testLenientNonFiniteDoubles() throws IOException {
     String json = "[NaN, -Infinity, Infinity]";
     JsonReader reader = new JsonReader(reader(json));
     reader.setLenient(true);
@@ -356,7 +385,8 @@ public void testLenientNonFiniteDoubles() throws IOException {
     reader.endArray();
   }
 
-  public void testLenientQuotedNonFiniteDoubles() throws IOException {
+  @Test
+  void testLenientQuotedNonFiniteDoubles() throws IOException {
     String json = "[\"NaN\", \"-Infinity\", \"Infinity\"]";
     JsonReader reader = new JsonReader(reader(json));
     reader.setLenient(true);
@@ -367,7 +397,8 @@ public void testLenientQuotedNonFiniteDoubles() throws IOException {
     reader.endArray();
   }
 
-  public void testStrictNonFiniteDoublesWithSkipValue() throws IOException {
+  @Test
+  void testStrictNonFiniteDoublesWithSkipValue() throws IOException {
     String json = "[NaN]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -378,7 +409,8 @@ public void testStrictNonFiniteDoublesWithSkipValue() throws IOException {
     }
   }
 
-  public void testLongs() throws IOException {
+  @Test
+  void testLongs() throws IOException {
     String json = "[0,0,0,"
         + "1,1,1,"
         + "-1,-1,-1,"
@@ -411,7 +443,9 @@ public void testLongs() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void disabled_testNumberWithOctalPrefix() throws IOException {
+  @Disabled
+  @Test
+  void testNumberWithOctalPrefix() throws IOException {
     String json = "[01]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -440,7 +474,8 @@ public void disabled_testNumberWithOctalPrefix() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testBooleans() throws IOException {
+  @Test
+  void testBooleans() throws IOException {
     JsonReader reader = new JsonReader(reader("[true,false]"));
     reader.beginArray();
     assertEquals(true, reader.nextBoolean());
@@ -449,7 +484,8 @@ public void testBooleans() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testPeekingUnquotedStringsPrefixedWithBooleans() throws IOException {
+  @Test
+  void testPeekingUnquotedStringsPrefixedWithBooleans() throws IOException {
     JsonReader reader = new JsonReader(reader("[truey]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -463,7 +499,8 @@ public void testPeekingUnquotedStringsPrefixedWithBooleans() throws IOException
     reader.endArray();
   }
 
-  public void testMalformedNumbers() throws IOException {
+  @Test
+  void testMalformedNumbers() throws IOException {
     assertNotANumber("-");
     assertNotANumber(".");
 
@@ -509,7 +546,8 @@ private void assertNotANumber(String s) throws IOException {
     reader.endArray();
   }
 
-  public void testPeekingUnquotedStringsPrefixedWithIntegers() throws IOException {
+  @Test
+  void testPeekingUnquotedStringsPrefixedWithIntegers() throws IOException {
     JsonReader reader = new JsonReader(reader("[12.34e5x]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -522,7 +560,8 @@ public void testPeekingUnquotedStringsPrefixedWithIntegers() throws IOException
     assertEquals("12.34e5x", reader.nextString());
   }
 
-  public void testPeekLongMinValue() throws IOException {
+  @Test
+  void testPeekLongMinValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[-9223372036854775808]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -530,7 +569,8 @@ public void testPeekLongMinValue() throws IOException {
     assertEquals(-9223372036854775808L, reader.nextLong());
   }
 
-  public void testPeekLongMaxValue() throws IOException {
+  @Test
+  void testPeekLongMaxValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[9223372036854775807]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -538,7 +578,8 @@ public void testPeekLongMaxValue() throws IOException {
     assertEquals(9223372036854775807L, reader.nextLong());
   }
 
-  public void testLongLargerThanMaxLongThatWrapsAround() throws IOException {
+  @Test
+  void testLongLargerThanMaxLongThatWrapsAround() throws IOException {
     JsonReader reader = new JsonReader(reader("[22233720368547758070]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -550,7 +591,8 @@ public void testLongLargerThanMaxLongThatWrapsAround() throws IOException {
     }
   }
 
-  public void testLongLargerThanMinLongThatWrapsAround() throws IOException {
+  @Test
+  void testLongLargerThanMinLongThatWrapsAround() throws IOException {
     JsonReader reader = new JsonReader(reader("[-22233720368547758070]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -561,24 +603,27 @@ public void testLongLargerThanMinLongThatWrapsAround() throws IOException {
     } catch (NumberFormatException expected) {
     }
   }
-  
+
   /**
    * Issue 1053, negative zero.
    * @throws Exception
    */
-  public void testNegativeZero() throws Exception {
-	  	JsonReader reader = new JsonReader(reader("[-0]"));
-	    reader.setLenient(false);
-	    reader.beginArray();
-	    assertEquals(NUMBER, reader.peek());
-	    assertEquals("-0", reader.nextString());
+  @Test
+  void testNegativeZero() throws Exception {
+        JsonReader reader = new JsonReader(reader("[-0]"));
+        reader.setLenient(false);
+        reader.beginArray();
+        assertEquals(NUMBER, reader.peek());
+        assertEquals("-0", reader.nextString());
   }
 
   /**
    * This test fails because there's no double for 9223372036854775808, and our
    * long parsing uses Double.parseDouble() for fractional values.
    */
-  public void disabled_testPeekLargerThanLongMaxValue() throws IOException {
+  @Disabled
+  @Test
+  void testPeekLargerThanLongMaxValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[9223372036854775808]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -594,7 +639,9 @@ public void disabled_testPeekLargerThanLongMaxValue() throws IOException {
    * This test fails because there's no double for -9223372036854775809, and our
    * long parsing uses Double.parseDouble() for fractional values.
    */
-  public void disabled_testPeekLargerThanLongMinValue() throws IOException {
+  @Disabled
+  @Test
+  void testPeekLargerThanLongMinValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[-9223372036854775809]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -611,7 +658,9 @@ public void disabled_testPeekLargerThanLongMinValue() throws IOException {
    * This test fails because there's no double for 9223372036854775806, and
    * our long parsing uses Double.parseDouble() for fractional values.
    */
-  public void disabled_testHighPrecisionLong() throws IOException {
+  @Disabled
+  @Test
+  void testHighPrecisionLong() throws IOException {
     String json = "[9223372036854775806.000]";
     JsonReader reader = new JsonReader(reader(json));
     reader.beginArray();
@@ -619,7 +668,8 @@ public void disabled_testHighPrecisionLong() throws IOException {
     reader.endArray();
   }
 
-  public void testPeekMuchLargerThanLongMinValue() throws IOException {
+  @Test
+  void testPeekMuchLargerThanLongMinValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[-92233720368547758080]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -632,7 +682,8 @@ public void testPeekMuchLargerThanLongMinValue() throws IOException {
     assertEquals(-92233720368547758080d, reader.nextDouble());
   }
 
-  public void testQuotedNumberWithEscape() throws IOException {
+  @Test
+  void testQuotedNumberWithEscape() throws IOException {
     JsonReader reader = new JsonReader(reader("[\"12\u00334\"]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -640,7 +691,8 @@ public void testQuotedNumberWithEscape() throws IOException {
     assertEquals(1234, reader.nextInt());
   }
 
-  public void testMixedCaseLiterals() throws IOException {
+  @Test
+  void testMixedCaseLiterals() throws IOException {
     JsonReader reader = new JsonReader(reader("[True,TruE,False,FALSE,NULL,nulL]"));
     reader.beginArray();
     assertEquals(true, reader.nextBoolean());
@@ -653,7 +705,8 @@ public void testMixedCaseLiterals() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testMissingValue() throws IOException {
+  @Test
+  void testMissingValue() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -664,7 +717,8 @@ public void testMissingValue() throws IOException {
     }
   }
 
-  public void testPrematureEndOfInput() throws IOException {
+  @Test
+  void testPrematureEndOfInput() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":true,"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -676,7 +730,8 @@ public void testPrematureEndOfInput() throws IOException {
     }
   }
 
-  public void testPrematurelyClosed() throws IOException {
+  @Test
+  void testPrematurelyClosed() throws IOException {
     try {
       JsonReader reader = new JsonReader(reader("{\"a\":[]}"));
       reader.beginObject();
@@ -706,7 +761,8 @@ public void testPrematurelyClosed() throws IOException {
     }
   }
 
-  public void testNextFailuresDoNotAdvance() throws IOException {
+  @Test
+  void testNextFailuresDoNotAdvance() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":true}"));
     reader.beginObject();
     try {
@@ -766,7 +822,8 @@ public void testNextFailuresDoNotAdvance() throws IOException {
     reader.close();
   }
 
-  public void testIntegerMismatchFailuresDoNotAdvance() throws IOException {
+  @Test
+  void testIntegerMismatchFailuresDoNotAdvance() throws IOException {
     JsonReader reader = new JsonReader(reader("[1.5]"));
     reader.beginArray();
     try {
@@ -778,7 +835,8 @@ public void testIntegerMismatchFailuresDoNotAdvance() throws IOException {
     reader.endArray();
   }
 
-  public void testStringNullIsNotNull() throws IOException {
+  @Test
+  void testStringNullIsNotNull() throws IOException {
     JsonReader reader = new JsonReader(reader("[\"null\"]"));
     reader.beginArray();
     try {
@@ -788,7 +846,8 @@ public void testStringNullIsNotNull() throws IOException {
     }
   }
 
-  public void testNullLiteralIsNotAString() throws IOException {
+  @Test
+  void testNullLiteralIsNotAString() throws IOException {
     JsonReader reader = new JsonReader(reader("[null]"));
     reader.beginArray();
     try {
@@ -798,7 +857,8 @@ public void testNullLiteralIsNotAString() throws IOException {
     }
   }
 
-  public void testStrictNameValueSeparator() throws IOException {
+  @Test
+  void testStrictNameValueSeparator() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\"=true}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -818,7 +878,8 @@ public void testStrictNameValueSeparator() throws IOException {
     }
   }
 
-  public void testLenientNameValueSeparator() throws IOException {
+  @Test
+  void testLenientNameValueSeparator() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\"=true}"));
     reader.setLenient(true);
     reader.beginObject();
@@ -832,7 +893,8 @@ public void testLenientNameValueSeparator() throws IOException {
     assertEquals(true, reader.nextBoolean());
   }
 
-  public void testStrictNameValueSeparatorWithSkipValue() throws IOException {
+  @Test
+  void testStrictNameValueSeparatorWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\"=true}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -852,7 +914,8 @@ public void testStrictNameValueSeparatorWithSkipValue() throws IOException {
     }
   }
 
-  public void testCommentsInStringValue() throws Exception {
+  @Test
+  void testCommentsInStringValue() throws Exception {
     JsonReader reader = new JsonReader(reader("[\"// comment\"]"));
     reader.beginArray();
     assertEquals("// comment", reader.nextString());
@@ -871,7 +934,8 @@ public void testCommentsInStringValue() throws Exception {
     reader.endObject();
   }
 
-  public void testStrictComments() throws IOException {
+  @Test
+  void testStrictComments() throws IOException {
     JsonReader reader = new JsonReader(reader("[// comment \n true]"));
     reader.beginArray();
     try {
@@ -897,7 +961,8 @@ public void testStrictComments() throws IOException {
     }
   }
 
-  public void testLenientComments() throws IOException {
+  @Test
+  void testLenientComments() throws IOException {
     JsonReader reader = new JsonReader(reader("[// comment \n true]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -914,7 +979,8 @@ public void testLenientComments() throws IOException {
     assertEquals(true, reader.nextBoolean());
   }
 
-  public void testStrictCommentsWithSkipValue() throws IOException {
+  @Test
+  void testStrictCommentsWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[// comment \n true]"));
     reader.beginArray();
     try {
@@ -940,7 +1006,8 @@ public void testStrictCommentsWithSkipValue() throws IOException {
     }
   }
 
-  public void testStrictUnquotedNames() throws IOException {
+  @Test
+  void testStrictUnquotedNames() throws IOException {
     JsonReader reader = new JsonReader(reader("{a:true}"));
     reader.beginObject();
     try {
@@ -950,14 +1017,16 @@ public void testStrictUnquotedNames() throws IOException {
     }
   }
 
-  public void testLenientUnquotedNames() throws IOException {
+  @Test
+  void testLenientUnquotedNames() throws IOException {
     JsonReader reader = new JsonReader(reader("{a:true}"));
     reader.setLenient(true);
     reader.beginObject();
     assertEquals("a", reader.nextName());
   }
 
-  public void testStrictUnquotedNamesWithSkipValue() throws IOException {
+  @Test
+  void testStrictUnquotedNamesWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("{a:true}"));
     reader.beginObject();
     try {
@@ -967,7 +1036,8 @@ public void testStrictUnquotedNamesWithSkipValue() throws IOException {
     }
   }
 
-  public void testStrictSingleQuotedNames() throws IOException {
+  @Test
+  void testStrictSingleQuotedNames() throws IOException {
     JsonReader reader = new JsonReader(reader("{'a':true}"));
     reader.beginObject();
     try {
@@ -977,14 +1047,16 @@ public void testStrictSingleQuotedNames() throws IOException {
     }
   }
 
-  public void testLenientSingleQuotedNames() throws IOException {
+  @Test
+  void testLenientSingleQuotedNames() throws IOException {
     JsonReader reader = new JsonReader(reader("{'a':true}"));
     reader.setLenient(true);
     reader.beginObject();
     assertEquals("a", reader.nextName());
   }
 
-  public void testStrictSingleQuotedNamesWithSkipValue() throws IOException {
+  @Test
+  void testStrictSingleQuotedNamesWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("{'a':true}"));
     reader.beginObject();
     try {
@@ -994,7 +1066,8 @@ public void testStrictSingleQuotedNamesWithSkipValue() throws IOException {
     }
   }
 
-  public void testStrictUnquotedStrings() throws IOException {
+  @Test
+  void testStrictUnquotedStrings() throws IOException {
     JsonReader reader = new JsonReader(reader("[a]"));
     reader.beginArray();
     try {
@@ -1004,7 +1077,8 @@ public void testStrictUnquotedStrings() throws IOException {
     }
   }
 
-  public void testStrictUnquotedStringsWithSkipValue() throws IOException {
+  @Test
+  void testStrictUnquotedStringsWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[a]"));
     reader.beginArray();
     try {
@@ -1014,14 +1088,16 @@ public void testStrictUnquotedStringsWithSkipValue() throws IOException {
     }
   }
 
-  public void testLenientUnquotedStrings() throws IOException {
+  @Test
+  void testLenientUnquotedStrings() throws IOException {
     JsonReader reader = new JsonReader(reader("[a]"));
     reader.setLenient(true);
     reader.beginArray();
     assertEquals("a", reader.nextString());
   }
 
-  public void testStrictSingleQuotedStrings() throws IOException {
+  @Test
+  void testStrictSingleQuotedStrings() throws IOException {
     JsonReader reader = new JsonReader(reader("['a']"));
     reader.beginArray();
     try {
@@ -1031,14 +1107,16 @@ public void testStrictSingleQuotedStrings() throws IOException {
     }
   }
 
-  public void testLenientSingleQuotedStrings() throws IOException {
+  @Test
+  void testLenientSingleQuotedStrings() throws IOException {
     JsonReader reader = new JsonReader(reader("['a']"));
     reader.setLenient(true);
     reader.beginArray();
     assertEquals("a", reader.nextString());
   }
 
-  public void testStrictSingleQuotedStringsWithSkipValue() throws IOException {
+  @Test
+  void testStrictSingleQuotedStringsWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("['a']"));
     reader.beginArray();
     try {
@@ -1048,7 +1126,8 @@ public void testStrictSingleQuotedStringsWithSkipValue() throws IOException {
     }
   }
 
-  public void testStrictSemicolonDelimitedArray() throws IOException {
+  @Test
+  void testStrictSemicolonDelimitedArray() throws IOException {
     JsonReader reader = new JsonReader(reader("[true;true]"));
     reader.beginArray();
     try {
@@ -1059,7 +1138,8 @@ public void testStrictSemicolonDelimitedArray() throws IOException {
     }
   }
 
-  public void testLenientSemicolonDelimitedArray() throws IOException {
+  @Test
+  void testLenientSemicolonDelimitedArray() throws IOException {
     JsonReader reader = new JsonReader(reader("[true;true]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1067,7 +1147,8 @@ public void testLenientSemicolonDelimitedArray() throws IOException {
     assertEquals(true, reader.nextBoolean());
   }
 
-  public void testStrictSemicolonDelimitedArrayWithSkipValue() throws IOException {
+  @Test
+  void testStrictSemicolonDelimitedArrayWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[true;true]"));
     reader.beginArray();
     try {
@@ -1078,7 +1159,8 @@ public void testStrictSemicolonDelimitedArrayWithSkipValue() throws IOException
     }
   }
 
-  public void testStrictSemicolonDelimitedNameValuePair() throws IOException {
+  @Test
+  void testStrictSemicolonDelimitedNameValuePair() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":true;\"b\":true}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -1090,7 +1172,8 @@ public void testStrictSemicolonDelimitedNameValuePair() throws IOException {
     }
   }
 
-  public void testLenientSemicolonDelimitedNameValuePair() throws IOException {
+  @Test
+  void testLenientSemicolonDelimitedNameValuePair() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":true;\"b\":true}"));
     reader.setLenient(true);
     reader.beginObject();
@@ -1099,7 +1182,8 @@ public void testLenientSemicolonDelimitedNameValuePair() throws IOException {
     assertEquals("b", reader.nextName());
   }
 
-  public void testStrictSemicolonDelimitedNameValuePairWithSkipValue() throws IOException {
+  @Test
+  void testStrictSemicolonDelimitedNameValuePairWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":true;\"b\":true}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -1111,7 +1195,8 @@ public void testStrictSemicolonDelimitedNameValuePairWithSkipValue() throws IOEx
     }
   }
 
-  public void testStrictUnnecessaryArraySeparators() throws IOException {
+  @Test
+  void testStrictUnnecessaryArraySeparators() throws IOException {
     JsonReader reader = new JsonReader(reader("[true,,true]"));
     reader.beginArray();
     assertEquals(true, reader.nextBoolean());
@@ -1147,7 +1232,8 @@ public void testStrictUnnecessaryArraySeparators() throws IOException {
     }
   }
 
-  public void testLenientUnnecessaryArraySeparators() throws IOException {
+  @Test
+  void testLenientUnnecessaryArraySeparators() throws IOException {
     JsonReader reader = new JsonReader(reader("[true,,true]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1178,7 +1264,8 @@ public void testLenientUnnecessaryArraySeparators() throws IOException {
     reader.endArray();
   }
 
-  public void testStrictUnnecessaryArraySeparatorsWithSkipValue() throws IOException {
+  @Test
+  void testStrictUnnecessaryArraySeparatorsWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[true,,true]"));
     reader.beginArray();
     assertEquals(true, reader.nextBoolean());
@@ -1214,7 +1301,8 @@ public void testStrictUnnecessaryArraySeparatorsWithSkipValue() throws IOExcepti
     }
   }
 
-  public void testStrictMultipleTopLevelValues() throws IOException {
+  @Test
+  void testStrictMultipleTopLevelValues() throws IOException {
     JsonReader reader = new JsonReader(reader("[] []"));
     reader.beginArray();
     reader.endArray();
@@ -1225,7 +1313,8 @@ public void testStrictMultipleTopLevelValues() throws IOException {
     }
   }
 
-  public void testLenientMultipleTopLevelValues() throws IOException {
+  @Test
+  void testLenientMultipleTopLevelValues() throws IOException {
     JsonReader reader = new JsonReader(reader("[] true {}"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1236,7 +1325,8 @@ public void testLenientMultipleTopLevelValues() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testStrictMultipleTopLevelValuesWithSkipValue() throws IOException {
+  @Test
+  void testStrictMultipleTopLevelValuesWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("[] []"));
     reader.beginArray();
     reader.endArray();
@@ -1247,7 +1337,8 @@ public void testStrictMultipleTopLevelValuesWithSkipValue() throws IOException {
     }
   }
 
-  public void testTopLevelValueTypes() throws IOException {
+  @Test
+  void testTopLevelValueTypes() throws IOException {
     JsonReader reader1 = new JsonReader(reader("true"));
     assertTrue(reader1.nextBoolean());
     assertEquals(JsonToken.END_DOCUMENT, reader1.peek());
@@ -1274,13 +1365,15 @@ public void testTopLevelValueTypes() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader6.peek());
   }
 
-  public void testTopLevelValueTypeWithSkipValue() throws IOException {
+  @Test
+  void testTopLevelValueTypeWithSkipValue() throws IOException {
     JsonReader reader = new JsonReader(reader("true"));
     reader.skipValue();
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testStrictNonExecutePrefix() {
+  @Test
+  void testStrictNonExecutePrefix() {
     JsonReader reader = new JsonReader(reader(")]}'\n []"));
     try {
       reader.beginArray();
@@ -1289,7 +1382,8 @@ public void testStrictNonExecutePrefix() {
     }
   }
 
-  public void testStrictNonExecutePrefixWithSkipValue() {
+  @Test
+  void testStrictNonExecutePrefixWithSkipValue() {
     JsonReader reader = new JsonReader(reader(")]}'\n []"));
     try {
       reader.skipValue();
@@ -1298,7 +1392,8 @@ public void testStrictNonExecutePrefixWithSkipValue() {
     }
   }
 
-  public void testLenientNonExecutePrefix() throws IOException {
+  @Test
+  void testLenientNonExecutePrefix() throws IOException {
     JsonReader reader = new JsonReader(reader(")]}'\n []"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1306,7 +1401,8 @@ public void testLenientNonExecutePrefix() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testLenientNonExecutePrefixWithLeadingWhitespace() throws IOException {
+  @Test
+  void testLenientNonExecutePrefixWithLeadingWhitespace() throws IOException {
     JsonReader reader = new JsonReader(reader("\r\n \t)]}'\n []"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1314,7 +1410,8 @@ public void testLenientNonExecutePrefixWithLeadingWhitespace() throws IOExceptio
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testLenientPartialNonExecutePrefix() {
+  @Test
+  void testLenientPartialNonExecutePrefix() {
     JsonReader reader = new JsonReader(reader(")]}' []"));
     reader.setLenient(true);
     try {
@@ -1325,13 +1422,15 @@ public void testLenientPartialNonExecutePrefix() {
     }
   }
 
-  public void testBomIgnoredAsFirstCharacterOfDocument() throws IOException {
+  @Test
+  void testBomIgnoredAsFirstCharacterOfDocument() throws IOException {
     JsonReader reader = new JsonReader(reader("\ufeff[]"));
     reader.beginArray();
     reader.endArray();
   }
 
-  public void testBomForbiddenAsOtherCharacterInDocument() throws IOException {
+  @Test
+  void testBomForbiddenAsOtherCharacterInDocument() throws IOException {
     JsonReader reader = new JsonReader(reader("[\ufeff]"));
     reader.beginArray();
     try {
@@ -1341,46 +1440,55 @@ public void testBomForbiddenAsOtherCharacterInDocument() throws IOException {
     }
   }
 
-  public void testFailWithPosition() throws IOException {
+  @Test
+  void testFailWithPosition() throws IOException {
     testFailWithPosition("Expected value at line 6 column 5 path $[1]",
         "[\n\n\n\n\n\"a\",}]");
   }
 
-  public void testFailWithPositionGreaterThanBufferSize() throws IOException {
+  @Test
+  void testFailWithPositionGreaterThanBufferSize() throws IOException {
     String spaces = repeat(' ', 8192);
     testFailWithPosition("Expected value at line 6 column 5 path $[1]",
         "[\n\n" + spaces + "\n\n\n\"a\",}]");
   }
 
-  public void testFailWithPositionOverSlashSlashEndOfLineComment() throws IOException {
+  @Test
+  void testFailWithPositionOverSlashSlashEndOfLineComment() throws IOException {
     testFailWithPosition("Expected value at line 5 column 6 path $[1]",
         "\n// foo\n\n//bar\r\n[\"a\",}");
   }
 
-  public void testFailWithPositionOverHashEndOfLineComment() throws IOException {
+  @Test
+  void testFailWithPositionOverHashEndOfLineComment() throws IOException {
     testFailWithPosition("Expected value at line 5 column 6 path $[1]",
         "\n# foo\n\n#bar\r\n[\"a\",}");
   }
 
-  public void testFailWithPositionOverCStyleComment() throws IOException {
+  @Test
+  void testFailWithPositionOverCStyleComment() throws IOException {
     testFailWithPosition("Expected value at line 6 column 12 path $[1]",
         "\n\n/* foo\n*\n*\r\nbar */[\"a\",}");
   }
 
-  public void testFailWithPositionOverQuotedString() throws IOException {
+  @Test
+  void testFailWithPositionOverQuotedString() throws IOException {
     testFailWithPosition("Expected value at line 5 column 3 path $[1]",
         "[\"foo\nbar\r\nbaz\n\",\n  }");
   }
 
-  public void testFailWithPositionOverUnquotedString() throws IOException {
+  @Test
+  void testFailWithPositionOverUnquotedString() throws IOException {
     testFailWithPosition("Expected value at line 5 column 2 path $[1]", "[\n\nabcd\n\n,}");
   }
 
-  public void testFailWithEscapedNewlineCharacter() throws IOException {
+  @Test
+  void testFailWithEscapedNewlineCharacter() throws IOException {
     testFailWithPosition("Expected value at line 5 column 3 path $[1]", "[\n\n\"\\\n\n\",}");
   }
 
-  public void testFailWithPositionIsOffsetByBom() throws IOException {
+  @Test
+  void testFailWithPositionIsOffsetByBom() throws IOException {
     testFailWithPosition("Expected value at line 1 column 6 path $[1]",
         "\ufeff[\"a\",}]");
   }
@@ -1411,7 +1519,8 @@ private void testFailWithPosition(String message, String json) throws IOExceptio
     }
   }
 
-  public void testFailWithPositionDeepPath() throws IOException {
+  @Test
+  void testFailWithPositionDeepPath() throws IOException {
     JsonReader reader = new JsonReader(reader("[1,{\"a\":[2,3,}"));
     reader.beginArray();
     reader.nextInt();
@@ -1428,7 +1537,8 @@ public void testFailWithPositionDeepPath() throws IOException {
     }
   }
 
-  public void testStrictVeryLongNumber() throws IOException {
+  @Test
+  void testStrictVeryLongNumber() throws IOException {
     JsonReader reader = new JsonReader(reader("[0." + repeat('9', 8192) + "]"));
     reader.beginArray();
     try {
@@ -1438,7 +1548,8 @@ public void testStrictVeryLongNumber() throws IOException {
     }
   }
 
-  public void testLenientVeryLongNumber() throws IOException {
+  @Test
+  void testLenientVeryLongNumber() throws IOException {
     JsonReader reader = new JsonReader(reader("[0." + repeat('9', 8192) + "]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1448,7 +1559,8 @@ public void testLenientVeryLongNumber() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testVeryLongUnquotedLiteral() throws IOException {
+  @Test
+  void testVeryLongUnquotedLiteral() throws IOException {
     String literal = "a" + repeat('b', 8192) + "c";
     JsonReader reader = new JsonReader(reader("[" + literal + "]"));
     reader.setLenient(true);
@@ -1457,7 +1569,8 @@ public void testVeryLongUnquotedLiteral() throws IOException {
     reader.endArray();
   }
 
-  public void testDeeplyNestedArrays() throws IOException {
+  @Test
+  void testDeeplyNestedArrays() throws IOException {
     // this is nested 40 levels deep; Gson is tuned for nesting is 30 levels deep or fewer
     JsonReader reader = new JsonReader(reader(
         "[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]"));
@@ -1472,7 +1585,8 @@ public void testDeeplyNestedArrays() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testDeeplyNestedObjects() throws IOException {
+  @Test
+  void testDeeplyNestedObjects() throws IOException {
     // Build a JSON document structured like {"a":{"a":{"a":{"a":true}}}}, but 40 levels deep
     String array = "{\"a\":%s}";
     String json = "true";
@@ -1495,7 +1609,8 @@ public void testDeeplyNestedObjects() throws IOException {
   }
 
   // http://code.google.com/p/google-gson/issues/detail?id=409
-  public void testStringEndingInSlash() throws IOException {
+  @Test
+  void testStringEndingInSlash() throws IOException {
     JsonReader reader = new JsonReader(reader("/"));
     reader.setLenient(true);
     try {
@@ -1505,7 +1620,8 @@ public void testStringEndingInSlash() throws IOException {
     }
   }
 
-  public void testDocumentWithCommentEndingInSlash() throws IOException {
+  @Test
+  void testDocumentWithCommentEndingInSlash() throws IOException {
     JsonReader reader = new JsonReader(reader("/* foo *//"));
     reader.setLenient(true);
     try {
@@ -1515,7 +1631,8 @@ public void testDocumentWithCommentEndingInSlash() throws IOException {
     }
   }
 
-  public void testStringWithLeadingSlash() throws IOException {
+  @Test
+  void testStringWithLeadingSlash() throws IOException {
     JsonReader reader = new JsonReader(reader("/x"));
     reader.setLenient(true);
     try {
@@ -1525,7 +1642,8 @@ public void testStringWithLeadingSlash() throws IOException {
     }
   }
 
-  public void testUnterminatedObject() throws IOException {
+  @Test
+  void testUnterminatedObject() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":\"android\"x"));
     reader.setLenient(true);
     reader.beginObject();
@@ -1538,7 +1656,8 @@ public void testUnterminatedObject() throws IOException {
     }
   }
 
-  public void testVeryLongQuotedString() throws IOException {
+  @Test
+  void testVeryLongQuotedString() throws IOException {
     char[] stringChars = new char[1024 * 16];
     Arrays.fill(stringChars, 'x');
     String string = new String(stringChars);
@@ -1549,7 +1668,8 @@ public void testVeryLongQuotedString() throws IOException {
     reader.endArray();
   }
 
-  public void testVeryLongUnquotedString() throws IOException {
+  @Test
+  void testVeryLongUnquotedString() throws IOException {
     char[] stringChars = new char[1024 * 16];
     Arrays.fill(stringChars, 'x');
     String string = new String(stringChars);
@@ -1561,7 +1681,8 @@ public void testVeryLongUnquotedString() throws IOException {
     reader.endArray();
   }
 
-  public void testVeryLongUnterminatedString() throws IOException {
+  @Test
+  void testVeryLongUnterminatedString() throws IOException {
     char[] stringChars = new char[1024 * 16];
     Arrays.fill(stringChars, 'x');
     String string = new String(stringChars);
@@ -1577,7 +1698,8 @@ public void testVeryLongUnterminatedString() throws IOException {
     }
   }
 
-  public void testSkipVeryLongUnquotedString() throws IOException {
+  @Test
+  void testSkipVeryLongUnquotedString() throws IOException {
     JsonReader reader = new JsonReader(reader("[" + repeat('x', 8192) + "]"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1585,49 +1707,56 @@ public void testSkipVeryLongUnquotedString() throws IOException {
     reader.endArray();
   }
 
-  public void testSkipTopLevelUnquotedString() throws IOException {
+  @Test
+  void testSkipTopLevelUnquotedString() throws IOException {
     JsonReader reader = new JsonReader(reader(repeat('x', 8192)));
     reader.setLenient(true);
     reader.skipValue();
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testSkipVeryLongQuotedString() throws IOException {
+  @Test
+  void testSkipVeryLongQuotedString() throws IOException {
     JsonReader reader = new JsonReader(reader("[\"" + repeat('x', 8192) + "\"]"));
     reader.beginArray();
     reader.skipValue();
     reader.endArray();
   }
 
-  public void testSkipTopLevelQuotedString() throws IOException {
+  @Test
+  void testSkipTopLevelQuotedString() throws IOException {
     JsonReader reader = new JsonReader(reader("\"" + repeat('x', 8192) + "\""));
     reader.setLenient(true);
     reader.skipValue();
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testStringAsNumberWithTruncatedExponent() throws IOException {
+  @Test
+  void testStringAsNumberWithTruncatedExponent() throws IOException {
     JsonReader reader = new JsonReader(reader("[123e]"));
     reader.setLenient(true);
     reader.beginArray();
     assertEquals(STRING, reader.peek());
   }
 
-  public void testStringAsNumberWithDigitAndNonDigitExponent() throws IOException {
+  @Test
+  void testStringAsNumberWithDigitAndNonDigitExponent() throws IOException {
     JsonReader reader = new JsonReader(reader("[123e4b]"));
     reader.setLenient(true);
     reader.beginArray();
     assertEquals(STRING, reader.peek());
   }
 
-  public void testStringAsNumberWithNonDigitExponent() throws IOException {
+  @Test
+  void testStringAsNumberWithNonDigitExponent() throws IOException {
     JsonReader reader = new JsonReader(reader("[123eb]"));
     reader.setLenient(true);
     reader.beginArray();
     assertEquals(STRING, reader.peek());
   }
 
-  public void testEmptyStringName() throws IOException {
+  @Test
+  void testEmptyStringName() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"\":true}"));
     reader.setLenient(true);
     assertEquals(BEGIN_OBJECT, reader.peek());
@@ -1641,7 +1770,8 @@ public void testEmptyStringName() throws IOException {
     assertEquals(JsonToken.END_DOCUMENT, reader.peek());
   }
 
-  public void testStrictExtraCommasInMaps() throws IOException {
+  @Test
+  void testStrictExtraCommasInMaps() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":\"b\",}"));
     reader.beginObject();
     assertEquals("a", reader.nextName());
@@ -1653,7 +1783,8 @@ public void testStrictExtraCommasInMaps() throws IOException {
     }
   }
 
-  public void testLenientExtraCommasInMaps() throws IOException {
+  @Test
+  void testLenientExtraCommasInMaps() throws IOException {
     JsonReader reader = new JsonReader(reader("{\"a\":\"b\",}"));
     reader.setLenient(true);
     reader.beginObject();
@@ -1672,7 +1803,8 @@ private String repeat(char c, int count) {
     return new String(array);
   }
 
-  public void testMalformedDocuments() throws IOException {
+  @Test
+  void testMalformedDocuments() throws IOException {
     assertDocument("{]", BEGIN_OBJECT, IOException.class);
     assertDocument("{,", BEGIN_OBJECT, IOException.class);
     assertDocument("{{", BEGIN_OBJECT, IOException.class);
@@ -1718,7 +1850,8 @@ public void testMalformedDocuments() throws IOException {
    * This test behave slightly differently in Gson 2.2 and earlier. It fails
    * during peek rather than during nextString().
    */
-  public void testUnterminatedStringFailure() throws IOException {
+  @Test
+  void testUnterminatedStringFailure() throws IOException {
     JsonReader reader = new JsonReader(reader("[\"string"));
     reader.setLenient(true);
     reader.beginArray();
@@ -1733,7 +1866,8 @@ public void testUnterminatedStringFailure() throws IOException {
   /**
    * Regression test for an issue with buffer filling and consumeNonExecutePrefix.
    */
-  public void testReadAcrossBuffers() throws IOException {
+  @Test
+  void testReadAcrossBuffers() throws IOException {
     StringBuilder sb = new StringBuilder('#');
     for (int i = 0; i < JsonReader.BUFFER_SIZE - 3; i++) {
       sb.append(' ');
diff --git a/gson/src/test/java/com/google/gson/stream/JsonWriterTest.java b/gson/src/test/java/com/google/gson/stream/JsonWriterTest.java
index 03ea7804c4..759b2a7c67 100644
--- a/gson/src/test/java/com/google/gson/stream/JsonWriterTest.java
+++ b/gson/src/test/java/com/google/gson/stream/JsonWriterTest.java
@@ -16,17 +16,20 @@
 
 package com.google.gson.stream;
 
-import junit.framework.TestCase;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import java.io.IOException;
 import java.io.StringWriter;
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import org.junit.jupiter.api.Test;
 
 @SuppressWarnings("resource")
-public final class JsonWriterTest extends TestCase {
+class JsonWriterTest {
 
-  public void testTopLevelValueTypes() throws IOException {
+  @Test
+  void testTopLevelValueTypes() throws IOException {
     StringWriter string1 = new StringWriter();
     JsonWriter writer1 = new JsonWriter(string1);
     writer1.value(true);
@@ -58,7 +61,8 @@ public void testTopLevelValueTypes() throws IOException {
     assertEquals("\"a\"", string5.toString());
   }
 
-  public void testInvalidTopLevelTypes() throws IOException {
+  @Test
+  void testInvalidTopLevelTypes() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.name("hello");
@@ -69,7 +73,8 @@ public void testInvalidTopLevelTypes() throws IOException {
     }
   }
 
-  public void testTwoNames() throws IOException {
+  @Test
+  void testTwoNames() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -81,7 +86,8 @@ public void testTwoNames() throws IOException {
     }
   }
 
-  public void testNameWithoutValue() throws IOException {
+  @Test
+  void testNameWithoutValue() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -93,7 +99,8 @@ public void testNameWithoutValue() throws IOException {
     }
   }
 
-  public void testValueWithoutName() throws IOException {
+  @Test
+  void testValueWithoutName() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -104,7 +111,8 @@ public void testValueWithoutName() throws IOException {
     }
   }
 
-  public void testMultipleTopLevelValues() throws IOException {
+  @Test
+  void testMultipleTopLevelValues() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray().endArray();
@@ -115,7 +123,8 @@ public void testMultipleTopLevelValues() throws IOException {
     }
   }
 
-  public void testBadNestingObject() throws IOException {
+  @Test
+  void testBadNestingObject() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -127,7 +136,8 @@ public void testBadNestingObject() throws IOException {
     }
   }
 
-  public void testBadNestingArray() throws IOException {
+  @Test
+  void testBadNestingArray() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -139,7 +149,8 @@ public void testBadNestingArray() throws IOException {
     }
   }
 
-  public void testNullName() throws IOException {
+  @Test
+  void testNullName() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -150,7 +161,8 @@ public void testNullName() throws IOException {
     }
   }
 
-  public void testNullStringValue() throws IOException {
+  @Test
+  void testNullStringValue() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -160,7 +172,8 @@ public void testNullStringValue() throws IOException {
     assertEquals("{\"a\":null}", stringWriter.toString());
   }
 
-  public void testJsonValue() throws IOException {
+  @Test
+  void testJsonValue() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -172,7 +185,8 @@ public void testJsonValue() throws IOException {
     assertEquals("{\"a\":{\"b\":true},\"c\":1}", stringWriter.toString());
   }
 
-  public void testNonFiniteDoubles() throws IOException {
+  @Test
+  void testNonFiniteDoubles() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -193,7 +207,8 @@ public void testNonFiniteDoubles() throws IOException {
     }
   }
 
-  public void testNonFiniteBoxedDoubles() throws IOException {
+  @Test
+  void testNonFiniteBoxedDoubles() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -214,7 +229,8 @@ public void testNonFiniteBoxedDoubles() throws IOException {
     }
   }
 
-  public void testNonFiniteDoublesWhenLenient() throws IOException {
+  @Test
+  void testNonFiniteDoublesWhenLenient() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.setLenient(true);
@@ -226,7 +242,8 @@ public void testNonFiniteDoublesWhenLenient() throws IOException {
     assertEquals("[NaN,-Infinity,Infinity]", stringWriter.toString());
   }
 
-  public void testNonFiniteBoxedDoublesWhenLenient() throws IOException {
+  @Test
+  void testNonFiniteBoxedDoublesWhenLenient() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.setLenient(true);
@@ -238,7 +255,8 @@ public void testNonFiniteBoxedDoublesWhenLenient() throws IOException {
     assertEquals("[NaN,-Infinity,Infinity]", stringWriter.toString());
   }
 
-  public void testDoubles() throws IOException {
+  @Test
+  void testDoubles() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -264,7 +282,8 @@ public void testDoubles() throws IOException {
         + "2.718281828459045]", stringWriter.toString());
   }
 
-  public void testLongs() throws IOException {
+  @Test
+  void testLongs() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -282,7 +301,8 @@ public void testLongs() throws IOException {
         + "9223372036854775807]", stringWriter.toString());
   }
 
-  public void testNumbers() throws IOException {
+  @Test
+  void testNumbers() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -298,7 +318,8 @@ public void testNumbers() throws IOException {
         + "3.141592653589793238462643383]", stringWriter.toString());
   }
 
-  public void testBooleans() throws IOException {
+  @Test
+  void testBooleans() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -308,7 +329,8 @@ public void testBooleans() throws IOException {
     assertEquals("[true,false]", stringWriter.toString());
   }
 
-  public void testBoxedBooleans() throws IOException {
+  @Test
+  void testBoxedBooleans() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -319,7 +341,8 @@ public void testBoxedBooleans() throws IOException {
     assertEquals("[true,false,null]", stringWriter.toString());
   }
 
-  public void testNulls() throws IOException {
+  @Test
+  void testNulls() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -328,7 +351,8 @@ public void testNulls() throws IOException {
     assertEquals("[null]", stringWriter.toString());
   }
 
-  public void testStrings() throws IOException {
+  @Test
+  void testStrings() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -371,7 +395,8 @@ public void testStrings() throws IOException {
         + "\"\\u0019\"]", stringWriter.toString());
   }
 
-  public void testUnicodeLineBreaksEscaped() throws IOException {
+  @Test
+  void testUnicodeLineBreaksEscaped() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -380,7 +405,8 @@ public void testUnicodeLineBreaksEscaped() throws IOException {
     assertEquals("[\"\\u2028 \\u2029\"]", stringWriter.toString());
   }
 
-  public void testEmptyArray() throws IOException {
+  @Test
+  void testEmptyArray() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -388,7 +414,8 @@ public void testEmptyArray() throws IOException {
     assertEquals("[]", stringWriter.toString());
   }
 
-  public void testEmptyObject() throws IOException {
+  @Test
+  void testEmptyObject() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -396,7 +423,8 @@ public void testEmptyObject() throws IOException {
     assertEquals("{}", stringWriter.toString());
   }
 
-  public void testObjectsInArrays() throws IOException {
+  @Test
+  void testObjectsInArrays() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginArray();
@@ -413,7 +441,8 @@ public void testObjectsInArrays() throws IOException {
         + "{\"c\":6,\"d\":true}]", stringWriter.toString());
   }
 
-  public void testArraysInObjects() throws IOException {
+  @Test
+  void testArraysInObjects() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -432,7 +461,8 @@ public void testArraysInObjects() throws IOException {
         + "\"b\":[6,true]}", stringWriter.toString());
   }
 
-  public void testDeepNestingArrays() throws IOException {
+  @Test
+  void testDeepNestingArrays() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     for (int i = 0; i < 20; i++) {
@@ -444,7 +474,8 @@ public void testDeepNestingArrays() throws IOException {
     assertEquals("[[[[[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]", stringWriter.toString());
   }
 
-  public void testDeepNestingObjects() throws IOException {
+  @Test
+  void testDeepNestingObjects() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -461,7 +492,8 @@ public void testDeepNestingObjects() throws IOException {
         + "}}}}}}}}}}}}}}}}}}}}}", stringWriter.toString());
   }
 
-  public void testRepeatedName() throws IOException {
+  @Test
+  void testRepeatedName() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.beginObject();
@@ -472,7 +504,8 @@ public void testRepeatedName() throws IOException {
     assertEquals("{\"a\":true,\"a\":false}", stringWriter.toString());
   }
 
-  public void testPrettyPrintObject() throws IOException {
+  @Test
+  void testPrettyPrintObject() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.setIndent("   ");
@@ -509,7 +542,8 @@ public void testPrettyPrintObject() throws IOException {
     assertEquals(expected, stringWriter.toString());
   }
 
-  public void testPrettyPrintArray() throws IOException {
+  @Test
+  void testPrettyPrintArray() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter jsonWriter = new JsonWriter(stringWriter);
     jsonWriter.setIndent("   ");
@@ -546,7 +580,8 @@ public void testPrettyPrintArray() throws IOException {
     assertEquals(expected, stringWriter.toString());
   }
 
-  public void testLenientWriterPermitsMultipleTopLevelValues() throws IOException {
+  @Test
+  void testLenientWriterPermitsMultipleTopLevelValues() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.setLenient(true);
@@ -558,7 +593,8 @@ public void testLenientWriterPermitsMultipleTopLevelValues() throws IOException
     assertEquals("[][]", stringWriter.toString());
   }
 
-  public void testStrictWriterDoesNotPermitMultipleTopLevelValues() throws IOException {
+  @Test
+  void testStrictWriterDoesNotPermitMultipleTopLevelValues() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
@@ -570,7 +606,8 @@ public void testStrictWriterDoesNotPermitMultipleTopLevelValues() throws IOExcep
     }
   }
 
-  public void testClosedWriterThrowsOnStructure() throws IOException {
+  @Test
+  void testClosedWriterThrowsOnStructure() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
@@ -598,7 +635,8 @@ public void testClosedWriterThrowsOnStructure() throws IOException {
     }
   }
 
-  public void testClosedWriterThrowsOnName() throws IOException {
+  @Test
+  void testClosedWriterThrowsOnName() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
@@ -611,7 +649,8 @@ public void testClosedWriterThrowsOnName() throws IOException {
     }
   }
 
-  public void testClosedWriterThrowsOnValue() throws IOException {
+  @Test
+  void testClosedWriterThrowsOnValue() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
@@ -624,7 +663,8 @@ public void testClosedWriterThrowsOnValue() throws IOException {
     }
   }
 
-  public void testClosedWriterThrowsOnFlush() throws IOException {
+  @Test
+  void testClosedWriterThrowsOnFlush() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
@@ -637,7 +677,8 @@ public void testClosedWriterThrowsOnFlush() throws IOException {
     }
   }
 
-  public void testWriterCloseIsIdempotent() throws IOException {
+  @Test
+  void testWriterCloseIsIdempotent() throws IOException {
     StringWriter stringWriter = new StringWriter();
     JsonWriter writer = new JsonWriter(stringWriter);
     writer.beginArray();
diff --git a/gson/src/test/resources/testcases-proguard.conf b/gson/src/test/resources/testcases-proguard.conf
index 19def61b00..21215c1ee8 100644
--- a/gson/src/test/resources/testcases-proguard.conf
+++ b/gson/src/test/resources/testcases-proguard.conf
@@ -13,8 +13,8 @@
 
 -keep enum com.google.gson.functional.EnumWithObfuscatedTest$Gender
 -keep class com.google.gson.functional.EnumWithObfuscatedTest {
-  public void test*();
-  protected void setUp();
+  void test*();
+  void setUp();
 }
 
 -dontwarn com.google.gson.functional.EnumWithObfuscatedTest
diff --git a/pom.xml b/pom.xml
index e8cee9222d..997a9c2ff7 100644
--- a/pom.xml
+++ b/pom.xml
@@ -29,6 +29,8 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <javaVersion>7</javaVersion>
+    <!-- Java version used for compiling and running unit tests -->
+    <testJavaVersion>11</testJavaVersion>
   </properties>
 
   <scm>
@@ -53,9 +55,9 @@
   <dependencyManagement>
     <dependencies>
       <dependency>
-        <groupId>junit</groupId>
-        <artifactId>junit</artifactId>
-        <version>4.13.2</version>
+        <groupId>org.junit.jupiter</groupId>
+        <artifactId>junit-jupiter</artifactId>
+        <version>5.8.2</version>
         <scope>test</scope>
       </dependency>
     </dependencies>
@@ -68,13 +70,41 @@
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
           <version>3.8.1</version>
+          <executions>
+            <execution>
+              <!-- Overwrite default-compile configuration -->
+              <id>default-compile</id>
+              <configuration>
+                <release>${javaVersion}</release>
+                <jdkToolchain>
+                  <version>[11,)</version>
+                </jdkToolchain>
+              </configuration>
+            </execution>
+            <execution>
+              <!-- Overwrite default-testCompile configuration -->
+              <id>default-testCompile</id>
+              <configuration>
+                <release>${testJavaVersion}</release>
+                <jdkToolchain>
+                  <version>[${testJavaVersion},)</version>
+                </jdkToolchain>
+              </configuration>
+            </execution>
+          </executions>
+        </plugin>
+
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <version>3.0.0-M5</version>
           <configuration>
-            <release>${javaVersion}</release>
             <jdkToolchain>
-              <version>[11,)</version>
+              <version>[${testJavaVersion},)</version>
             </jdkToolchain>
           </configuration>
         </plugin>
+
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
@@ -99,6 +129,7 @@
             <detectOfflineLinks>false</detectOfflineLinks>
           </configuration>
         </plugin>
+
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-jar-plugin</artifactId>
diff --git a/proto/pom.xml b/proto/pom.xml
index aa13c952a0..fc043c6a56 100644
--- a/proto/pom.xml
+++ b/proto/pom.xml
@@ -41,8 +41,8 @@
     </dependency>
 
     <dependency>
-      <groupId>junit</groupId>
-      <artifactId>junit</artifactId>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
 
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
index 0a508f9d6d..3f08c6f6df 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithAnnotationsTest.java
@@ -31,21 +31,21 @@
 import com.google.gson.protobuf.generated.Bag.ProtoWithAnnotations.InnerMessage.Data;
 import com.google.gson.protobuf.generated.Bag.ProtoWithAnnotations.InnerMessage.Type;
 import com.google.protobuf.GeneratedMessageV3;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for protocol buffers using annotations for field names and enum values.
  *
  * @author Emmanuel Cron
  */
-public class ProtosWithAnnotationsTest extends TestCase {
+class ProtosWithAnnotationsTest {
   private Gson gson;
   private Gson gsonWithEnumNumbers;
   private Gson gsonWithLowerHyphen;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     ProtoTypeAdapter.Builder protoTypeAdapter = ProtoTypeAdapter.newBuilder()
         .setEnumSerialization(EnumSerialization.NAME)
         .addSerializedNameExtension(Annotations.serializedName)
@@ -65,7 +65,8 @@ protected void setUp() throws Exception {
         .create();
   }
 
-  public void testProtoWithAnnotations_deserialize() {
+  @Test
+  void testProtoWithAnnotations_deserialize() {
     String json = String.format("{  %n"
         + "   \"id\":\"41e5e7fd6065d101b97018a465ffff01\",%n"
         + "   \"expiration_date\":{  %n"
@@ -142,7 +143,8 @@ public void testProtoWithAnnotations_deserialize() {
         + "}]}}");
   }
 
-  public void testProtoWithAnnotations_deserializeUnknownEnumValue() {
+  @Test
+  void testProtoWithAnnotations_deserializeUnknownEnumValue() {
     String json = String.format("{  %n"
         + "   \"content\":\"UNKNOWN\"%n"
         + "}");
@@ -150,7 +152,8 @@ public void testProtoWithAnnotations_deserializeUnknownEnumValue() {
     assertThat(proto.getContent()).isEqualTo(Type.UNKNOWN);
   }
 
-  public void testProtoWithAnnotations_deserializeUnrecognizedEnumValue() {
+  @Test
+  void testProtoWithAnnotations_deserializeUnrecognizedEnumValue() {
     String json = String.format("{  %n"
         + "   \"content\":\"UNRECOGNIZED\"%n"
         + "}");
@@ -162,7 +165,8 @@ public void testProtoWithAnnotations_deserializeUnrecognizedEnumValue() {
     }
   }
 
-  public void testProtoWithAnnotations_deserializeWithEnumNumbers() {
+  @Test
+  void testProtoWithAnnotations_deserializeWithEnumNumbers() {
     String json = String.format("{  %n"
         + "   \"content\":\"0\"%n"
         + "}");
@@ -180,7 +184,8 @@ public void testProtoWithAnnotations_deserializeWithEnumNumbers() {
     assertThat(rebuilt).isEqualTo("{\"content\":2}");
   }
 
-  public void testProtoWithAnnotations_serialize() {
+  @Test
+  void testProtoWithAnnotations_serialize() {
     ProtoWithAnnotations proto = ProtoWithAnnotations.newBuilder()
         .setId("09f3j20839h032y0329hf30932h0nffn")
         .setOuterMessage(OuterMessage.newBuilder()
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
index 8e59d5d1e9..a3e80bfaa3 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithComplexAndRepeatedFieldsTest.java
@@ -15,6 +15,9 @@
  */
 package com.google.gson.protobuf.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.common.base.CaseFormat;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -25,20 +28,20 @@
 import com.google.gson.protobuf.generated.Bag.ProtoWithRepeatedFields;
 import com.google.gson.protobuf.generated.Bag.SimpleProto;
 import com.google.protobuf.GeneratedMessageV3;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
 /**
  * Functional tests for protocol buffers using complex and repeated fields
  *
  * @author Inderjeet Singh
  */
-public class ProtosWithComplexAndRepeatedFieldsTest extends TestCase {
+class ProtosWithComplexAndRepeatedFieldsTest {
   private Gson gson;
   private Gson upperCamelGson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson =
         new GsonBuilder()
             .registerTypeHierarchyAdapter(GeneratedMessageV3.class,
@@ -56,7 +59,8 @@ protected void setUp() throws Exception {
             .create();
   }
 
-  public void testSerializeRepeatedFields() {
+  @Test
+  void testSerializeRepeatedFields() {
     ProtoWithRepeatedFields proto = ProtoWithRepeatedFields.newBuilder()
       .addNumbers(2)
       .addNumbers(3)
@@ -69,7 +73,8 @@ public void testSerializeRepeatedFields() {
     assertTrue(json.contains("count"));
   }
 
-  public void testDeserializeRepeatedFieldsProto() {
+  @Test
+  void testDeserializeRepeatedFieldsProto() {
     String json = "{numbers:[4,6],simples:[{msg:'bar'},{count:7}]}";
     ProtoWithRepeatedFields proto =
       gson.fromJson(json, ProtoWithRepeatedFields.class);
@@ -79,7 +84,8 @@ public void testDeserializeRepeatedFieldsProto() {
     assertEquals(7, proto.getSimples(1).getCount());
   }
 
-  public void testSerializeDifferentCaseFormat() {
+  @Test
+  void testSerializeDifferentCaseFormat() {
     final ProtoWithDifferentCaseFormat proto =
       ProtoWithDifferentCaseFormat.newBuilder()
         .setAnotherField("foo")
@@ -90,7 +96,8 @@ public void testSerializeDifferentCaseFormat() {
     assertEquals("bar", json.get("NameThatTestsCaseFormat").getAsJsonArray().get(0).getAsString());
   }
 
-  public void testDeserializeDifferentCaseFormat() {
+  @Test
+  void testDeserializeDifferentCaseFormat() {
     final String json = "{NameThatTestsCaseFormat:['bar'],AnotherField:'foo'}";
     ProtoWithDifferentCaseFormat proto =
       upperCamelGson.fromJson(json, ProtoWithDifferentCaseFormat.class);
diff --git a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
index 2e9d0e1733..72c880ea88 100644
--- a/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
+++ b/proto/src/test/java/com/google/gson/protobuf/functional/ProtosWithPrimitiveTypesTest.java
@@ -15,6 +15,10 @@
  */
 package com.google.gson.protobuf.functional;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.protobuf.ProtoTypeAdapter;
@@ -22,14 +26,14 @@
 import com.google.gson.protobuf.generated.Bag.SimpleProto;
 import com.google.protobuf.Descriptors.Descriptor;
 import com.google.protobuf.GeneratedMessageV3;
-import junit.framework.TestCase;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
 
-public class ProtosWithPrimitiveTypesTest extends TestCase {
+class ProtosWithPrimitiveTypesTest {
   private Gson gson;
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
+  @BeforeEach
+  void setUp() throws Exception {
     gson = new GsonBuilder().registerTypeHierarchyAdapter(
       GeneratedMessageV3.class, ProtoTypeAdapter.newBuilder()
           .setEnumSerialization(EnumSerialization.NUMBER)
@@ -37,19 +41,22 @@ protected void setUp() throws Exception {
       .create();
   }
 
-  public void testSerializeEmptyProto() {
+  @Test
+  void testSerializeEmptyProto() {
     SimpleProto proto = SimpleProto.newBuilder().build();
     String json = gson.toJson(proto);
     assertEquals("{}", json);
   }
 
-  public void testDeserializeEmptyProto() {
+  @Test
+  void testDeserializeEmptyProto() {
     SimpleProto proto = gson.fromJson("{}", SimpleProto.class);
     assertFalse(proto.hasCount());
     assertFalse(proto.hasMsg());
   }
 
-  public void testSerializeProto() {
+  @Test
+  void testSerializeProto() {
     Descriptor descriptor = SimpleProto.getDescriptor();
     SimpleProto proto = SimpleProto.newBuilder()
       .setCount(3)
@@ -60,13 +67,15 @@ public void testSerializeProto() {
     assertTrue(json.contains("\"count\":3"));
   }
 
-  public void testDeserializeProto() {
+  @Test
+  void testDeserializeProto() {
     SimpleProto proto = gson.fromJson("{msg:'foo',count:3}", SimpleProto.class);
     assertEquals("foo", proto.getMsg());
     assertEquals(3, proto.getCount());
   }
 
-  public void testDeserializeWithExplicitNullValue() {
+  @Test
+  void testDeserializeWithExplicitNullValue() {
     SimpleProto proto = gson.fromJson("{msg:'foo',count:null}", SimpleProto.class);
     assertEquals("foo", proto.getMsg());
     assertEquals(0, proto.getCount());