From 437d29e034c039844bde3d9988b346dadc3a13fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alaksiej=20=C5=A0=C4=8Darbaty?=
 <hahaha.funny.yellow.dog@gmail.com>
Date: Fri, 25 Aug 2023 16:31:36 +0200
Subject: [PATCH] assertInstanceOf methods accept nullable values

Issue: #1866
---
 .../src/main/kotlin/org/junit/jupiter/api/Assertions.kt  | 6 +++---
 .../org/junit/jupiter/api/KotlinAssertionsTests.kt       | 9 +++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

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
index 0db69152047..89857de0e9a 100644
--- 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
@@ -244,7 +244,7 @@ fun assertNotNull(actual: Any?, messageSupplier: () -> String) {
  * @see Assertions.assertInstanceOf
  */
 @API(since = "5.11", status = EXPERIMENTAL)
-inline fun <reified T : Any> assertInstanceOf(actual: Any) {
+inline fun <reified T : Any> assertInstanceOf(actual: Any?) {
     contract {
         returns() implies (actual is T)
     }
@@ -265,7 +265,7 @@ inline fun <reified T : Any> assertInstanceOf(actual: Any) {
  * @see Assertions.assertInstanceOf
  */
 @API(since = "5.11", status = EXPERIMENTAL)
-inline fun <reified T : Any> assertInstanceOf(actual: Any, message: String) {
+inline fun <reified T : Any> assertInstanceOf(actual: Any?, message: String) {
     contract {
         returns() implies (actual is T)
     }
@@ -286,7 +286,7 @@ inline fun <reified T : Any> assertInstanceOf(actual: Any, message: String) {
  * @see Assertions.assertInstanceOf
  */
 @API(since = "5.11", status = EXPERIMENTAL)
-inline fun <reified T : Any> assertInstanceOf(actual: Any, noinline messageSupplier: () -> String) {
+inline fun <reified T : Any> assertInstanceOf(actual: Any?, noinline messageSupplier: () -> String) {
     contract {
         returns() implies (actual is T)
 
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
index b2dc4988301..b40859d2751 100644
--- 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
@@ -236,6 +236,15 @@ class KotlinAssertionsTests {
         assertFalse(string.isEmpty()) // smart cast to a String object
     }
 
+    @Test
+    fun `assertInstanceOf with a null value`() {
+        val error = assertThrows<AssertionFailedError> {
+            assertInstanceOf<String>(null)
+        }
+
+        assertMessageStartsWith(error, "Unexpected null value")
+    }
+
     @Test
     fun `assertDoesNotThrow with value initialization in lambda`() {
         val value: Int