kotlin-test: add assertIs and assertNotIs assertions KT-45296

libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Assertions.kt

@@ -17,6 +17,7 @@ import kotlin.internal.*
 import kotlin.jvm.JvmName
 import kotlin.native.concurrent.ThreadLocal
 import kotlin.reflect.KClass
+import kotlin.reflect.typeOf
 
 /**
  * Current adapter providing assertion implementations
@@ -76,6 +77,31 @@ fun <@OnlyInputTypes T> assertNotSame(illegal: T, actual: T, message: String? =
     asserter.assertNotSame(message, illegal, actual)
 }
 
+/**
+ * Asserts that [value] is of type [T], with an optional [message].
+ *
+ * Note that due to type erasure the type check may be partial (e.g. assertIs<List<String>>(value)
+ * only checks for the class being [List] and not the type of its elements because it's erased).
+ */
+@SinceKotlin("1.5")
+@InlineOnly
+inline fun <reified T> assertIs(value: Any?, message: String? = null) {
+    contract { returns() implies (value is T) }
+    asserter.assertTrue({ messagePrefix(message) + "Expected value to be of type <${typeOf<T>()}>, actual <${value?.let { it::class }}>." }, value is T)
+}
+
+/**
+ * Asserts that [value] is not of type [T], with an optional [message].
+ *
+ * Note that due to type erasure the type check may be partial (e.g. assertNotIs<List<String>>(value)
+ * only checks for the class being [List] and not the type of its elements because it's erased).
+ */
+@SinceKotlin("1.5")
+@InlineOnly
+inline fun <reified T> assertNotIs(value: Any?, message: String? = null) {
+    asserter.assertFalse({ messagePrefix(message) + "Expected value to not be of type <${typeOf<T>()}>" }, value is T)
+}
+
 /** Asserts that the [actual] value is not `null`, with an optional [message]. */
 fun <T : Any> assertNotNull(actual: T?, message: String? = null): T {
     contract { returns() implies (actual != null) }

libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt

@@ -5,6 +5,7 @@
 
 package kotlin.test
 
+@PublishedApi // called from inline assert functions
 internal fun messagePrefix(message: String?) = if (message == null) "" else "$message. "
 internal expect fun lookupAsserter(): Asserter
 

libraries/kotlin.test/common/src/test/kotlin/kotlin/test/tests/BasicAssertionsTest.kt

@@ -205,6 +205,33 @@ class BasicAssertionsTest {
     fun testExpectFails() {
         checkFailedAssertion { expect(1) { 2 } }
     }
+
+    @Test
+    fun testAssertIs() {
+        val s: Any = "test"
+        assertIs<String>(s)
+        assertEquals(4, s.length)
+    }
+
+    @Test
+    fun testAssertIsFails() {
+        val error = checkFailedAssertion { assertIs<Int>("test") }
+        assertTrue(error.message.startsWith("Expected value to be of type"))
+        assertTrue(error.message.contains("Int"))
+        assertTrue(error.message.contains("String"))
+    }
+
+    @Test
+    fun testAssertNotIs() {
+        assertNotIs<Int>("test")
+    }
+
+    @Test
+    fun testAssertNotIsFails() {
+        val error = checkFailedAssertion { assertNotIs<Int>(1) }
+        assertTrue(error.message.startsWith("Expected value to not be of type"))
+        assertTrue(error.message.contains("Int"))
+    }
 }