Add assertInstanceOf methods

Added `assertInstanceOf` assertions with upcasting contracts Issue: junit-team#1866
awelless · Aug 25, 2023 · 544b4e1 · 544b4e1
1 parent e427978
commit 544b4e1
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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
@@ -231,6 +231,71 @@ fun assertNotNull(actual: Any?, messageSupplier: () -> String) {
     Assertions.assertNotNull(actual, messageSupplier)
 }
 
+/**
+ * Example usage:
+ * ```kotlin
+ * val string: Any = ...
+ *
+ * assertInstanceOf<String>(string)
+ *
+ * // compiler smart casts string to a String object
+ * assertTrue(string.isNotEmpty())
+ * ```
+ * @see Assertions.assertInstanceOf
+ */
+@API(since = "5.11", status = EXPERIMENTAL)
+inline fun <reified T : Any> assertInstanceOf(actual: Any) {
+    contract {
+        returns() implies (actual is T)
+    }
+
+    Assertions.assertInstanceOf(T::class.java, actual)
+}
+
+/**
+ * Example usage:
+ * ```kotlin
+ * val string: Any = ...
+ *
+ * assertInstanceOf<String>(string, "Should be a String")
+ *
+ * // compiler smart casts string to a String object
+ * assertTrue(string.isNotEmpty())
+ * ```
+ * @see Assertions.assertInstanceOf
+ */
+@API(since = "5.11", status = EXPERIMENTAL)
+inline fun <reified T : Any> assertInstanceOf(actual: Any, message: String) {
+    contract {
+        returns() implies (actual is T)
+    }
+
+    Assertions.assertInstanceOf(T::class.java, actual, message)
+}
+
+/**
+ * Example usage:
+ * ```kotlin
+ * val string: Any = ...
+ *
+ * assertInstanceOf<String>(string) { "Should be a String" }
+ *
+ * // compiler smart casts string to a String object
+ * assertTrue(string.isNotEmpty())
+ * ```
+ * @see Assertions.assertInstanceOf
+ */
+@API(since = "5.11", status = EXPERIMENTAL)
+inline fun <reified T : Any> assertInstanceOf(actual: Any, noinline messageSupplier: () -> String) {
+    contract {
+        returns() implies (actual is T)
+
+        callsInPlace(messageSupplier, AT_MOST_ONCE)
+    }
+
+    Assertions.assertInstanceOf(T::class.java, actual, messageSupplier)
+}
+
 /**
  * Example usage:
  * ```kotlin

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
@@ -228,6 +228,14 @@ class KotlinAssertionsTests {
         // nullableString?.isEmpty()
     }
 
+    @Test
+    fun `assertInstanceOf with compiler smart cast`() {
+        val string: Any = "string"
+
+        assertInstanceOf<String>(string)
+        assertFalse(string.isEmpty()) // smart cast to a String object
+    }
+
     @Test
     fun `assertDoesNotThrow with value initialization in lambda`() {
         val value: Int