Add stubber (top-level) doSuspendableAnswer()

mockito-kotlin/src/main/kotlin/org/mockito/kotlin/Stubber.kt

@@ -28,13 +28,19 @@ package org.mockito.kotlin
 import kotlinx.coroutines.runBlocking
 import org.mockito.Mockito
 import org.mockito.invocation.InvocationOnMock
+import org.mockito.kotlin.internal.SuspendableAnswer
+import org.mockito.stubbing.OngoingStubbing
 import org.mockito.stubbing.Stubber
 import kotlin.reflect.KClass
 
 fun <T> doAnswer(answer: (InvocationOnMock) -> T?): Stubber {
     return Mockito.doAnswer { answer(it) }!!
 }
 
+fun <T> doSuspendableAnswer(answer: suspend (KInvocationOnMock) -> T?): Stubber {
+    return Mockito.doAnswer(SuspendableAnswer(answer))
+}
+
 fun doCallRealMethod(): Stubber {
     return Mockito.doCallRealMethod()!!
 }

mockito-kotlin/src/test/kotlin/test/CoroutinesTest.kt

@@ -294,6 +294,100 @@ class CoroutinesTest {
         }
     }
 
+    @Test
+    fun stubberAnswerWithSuspendFunction() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        doSuspendableAnswer {
+            withContext(Dispatchers.Default) { it.getArgument<Int>(0) }
+        }.whenever(fixture).suspendingWithArg(any())
+
+        assertEquals(5, fixture.suspendingWithArg(5))
+    }
+
+    @Test
+    fun stubberCallFromSuspendFunction() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        doSuspendableAnswer {
+            withContext(Dispatchers.Default) { it.getArgument<Int>(0) }
+        }.whenever(fixture).suspendingWithArg(any())
+
+        val result = async {
+            val answer = fixture.suspendingWithArg(5)
+
+            Result.success(answer)
+        }
+
+        assertEquals(5, result.await().getOrThrow())
+    }
+
+    @Test
+    fun stubberCallFromActor() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        doSuspendableAnswer {
+            withContext(Dispatchers.Default) { it.getArgument<Int>(0) }
+        }.whenever(fixture).suspendingWithArg(any())
+
+        val actor = actor<Optional<Int>> {
+            for (element in channel) {
+                fixture.suspendingWithArg(element.get())
+            }
+        }
+
+        actor.send(Optional.of(10))
+        actor.close()
+
+        verify(fixture).suspendingWithArg(10)
+
+        Unit
+    }
+
+    @Test
+    fun stubberAnswerWithSuspendFunctionWithoutArgs() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        doSuspendableAnswer {
+            withContext(Dispatchers.Default) { 42 }
+        }.whenever(fixture).suspending()
+
+        assertEquals(42, fixture.suspending())
+    }
+
+    @Test
+    fun stubberAnswerWithSuspendFunctionWithDestructuredArgs() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        doSuspendableAnswer { (i: Int) ->
+            withContext(Dispatchers.Default) { i }
+        }.whenever(fixture).suspendingWithArg(any())
+
+        assertEquals(5, fixture.suspendingWithArg(5))
+    }
+
+    @Test
+    fun stubberWillAnswerWithControlledSuspend() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        val job = Job()
+
+        doSuspendableAnswer {
+            job.join()
+            5
+        }.whenever(fixture).suspending()
+
+        val asyncTask = async {
+            fixture.suspending()
+        }
+
+        job.complete()
+
+        withTimeout(100) {
+            assertEquals(5, asyncTask.await())
+        }
+    }
+
     @Test
     fun inOrderRemainsCompatible() {
         /* Given */