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());