Add Kotlin friendly assertInstanceOf assertions

Resolves #3353 Signed-off-by: Björn Michael <b.michael@gmx.de>
junit-team · Dec 30, 2023 · bedba01 · bedba01
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diff --git a/documentation/src/docs/asciidoc/release-notes/release-notes-5.10.1.adoc b/documentation/src/docs/asciidoc/release-notes/release-notes-5.10.1.adoc
@@ -50,7 +50,8 @@ JUnit repository on GitHub.
 * Improved Javadoc for `Assertions.assertTimeoutPreemptively` regarding thread interrupt.
 * Documentation for `@Disabled` and conditional annotations now explicitly explains that
   such annotations are not inherited by subclasses.
-
+* New `assertInstanceOf` methods added for Kotlin following up with similar Java
+  `assertInstanceOf` methods introduced in `5.8` version.
 
 [[release-notes-5.10.1-junit-vintage]]
 === JUnit Vintage

diff --git a/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt b/junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt
@@ -287,3 +287,23 @@ fun <R> assertTimeoutPreemptively(timeout: Duration, message: String, executable
 @API(status = EXPERIMENTAL, since = "5.5")
 fun <R> assertTimeoutPreemptively(timeout: Duration, message: () -> String, executable: () -> R): R =
     Assertions.assertTimeoutPreemptively(timeout, executable, message)
+
+/**
+ * Example usage:
+ * ```kotlin
+ * assertInstanceOf<RandomAccess>(list, "List should support fast random access")
+ * ```
+ * @see Assertions.assertInstanceOf
+ * @since 5.10.1
+ */
+@API(status = EXPERIMENTAL, since = "5.10.1")
+inline fun <reified T : Any> assertInstanceOf(actualValue: Any?, message: String? = null): T =
+    Assertions.assertInstanceOf(T::class.java, actualValue, message)
+
+/*
+ * @see Assertions.assertInstanceOf
+ * @since 5.10.1
+ */
+@API(status = EXPERIMENTAL, since = "5.10.1")
+inline fun <reified T : Any> assertInstanceOf(actualValue: Any?, noinline message: () -> String): T =
+    Assertions.assertInstanceOf(T::class.java, actualValue, message)
diff --git a/junit-jupiter-engine/src/test/kotlin/org/junit/jupiter/api/KotlinAssertionsTests.kt b/junit-jupiter-engine/src/test/kotlin/org/junit/jupiter/api/KotlinAssertionsTests.kt
@@ -211,6 +211,29 @@ class KotlinAssertionsTests {
         assertMessageStartsWith(error, assertionMessage)
     }
 
+    @Test
+    fun assertInstanceOf() {
+        assertInstanceOf<RandomAccess>(listOf("whatever"))
+        assertInstanceOf<RandomAccess>(listOf("whatever"), "No random access")
+        assertInstanceOf<RandomAccess>(listOf("whatever")) { "No random access" }
+    }
+
+    @Test
+    fun `assertInstanceOf fails wrong type value`() {
+        val result = assertThrows<AssertionError> {
+            assertInstanceOf<String>(StringBuilder(), "Should be a String")
+        }
+        assertMessageStartsWith(result, "Should be a String")
+    }
+
+    @Test
+    fun `assertInstanceOf fails null value`() {
+        val result = assertThrows<AssertionError> {
+            assertInstanceOf<String>(null, "Should be a String")
+        }
+        assertMessageStartsWith(result, "Should be a String")
+    }
+
     companion object {
         fun assertExpectedExceptionTypes(
             multipleFailuresError: MultipleFailuresError,