Add suspend answer; Fix #346

This code was inspired by:
- Java wrapper part: https://github.com/square/retrofit/blob/8c93b59dbc57841959f5237cb141ce0b3c18b778/retrofit/src/main/java/retrofit2/HttpServiceMethod.java#L168
- Kotlin wrapper part: https://github.com/square/retrofit/blob/8c93b59dbc57841959f5237cb141ce0b3c18b778/retrofit/src/main/java/retrofit2/KotlinExtensions.kt#L83-L98

Author: neworld

mockito-kotlin/src/main/java/com/nhaarman/mockitokotlin2/internal/JavaSuspendWrapper.java

@@ -0,0 +1,48 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2018 Niek Haarman
+ * Copyright (c) 2007 Mockito contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.nhaarman.mockitokotlin2.internal;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.mockito.invocation.InvocationOnMock;
+
+import kotlin.coroutines.Continuation;
+import kotlin.jvm.functions.Function2;
+
+/**
+ * This wrapper is needed, because kotlin does not allow explicit call suspend function providing Continuation.
+ * But interoperability via Java allows it.
+ */
+public class JavaSuspendWrapper {
+    /**
+     * @param function accepting Object, otherwise kotlin does not allow pass suspending lambda
+     */
+    @Nullable
+    public static <T> Object wrapSuspend(@NotNull Continuation<?> continuation, @NotNull InvocationOnMock invocationOnMock, @NotNull Object function) {
+        Function2<InvocationOnMock, Continuation<? super T>, Object> realFunction = (Function2<InvocationOnMock, Continuation<? super T>, Object>) function;
+        return KotlinSuspendWrapperKt.wrapSuspend(realFunction, invocationOnMock, (Continuation<Object>) continuation);
+    }
+}

mockito-kotlin/src/main/kotlin/com/nhaarman/mockitokotlin2/OngoingStubbing.kt

@@ -25,11 +25,13 @@
 
 package com.nhaarman.mockitokotlin2
 
+import com.nhaarman.mockitokotlin2.internal.JavaSuspendWrapper
 import org.mockito.Mockito
+import org.mockito.internal.invocation.InterceptedInvocation
 import org.mockito.invocation.InvocationOnMock
 import org.mockito.stubbing.Answer
 import org.mockito.stubbing.OngoingStubbing
-import kotlin.DeprecationLevel.ERROR
+import kotlin.coroutines.Continuation
 import kotlin.reflect.KClass
 
 
@@ -124,3 +126,15 @@ infix fun <T> OngoingStubbing<T>.doAnswer(answer: Answer<*>): OngoingStubbing<T>
 infix fun <T> OngoingStubbing<T>.doAnswer(answer: (InvocationOnMock) -> T?): OngoingStubbing<T> {
     return thenAnswer(answer)
 }
+
+infix fun <T> OngoingStubbing<T>.willAnswer(answer: suspend (InvocationOnMock) -> T?): OngoingStubbing<T> {
+    return doAnswer {
+        //all suspend functions/lambdas has Continuation as the last argument.
+        //InvocationOnMock does not see last argument
+        val rawInvocation = it as InterceptedInvocation
+        val continuation = rawInvocation.rawArguments[1] as Continuation<*>
+
+        //This method sometimes returns different object. T? is needed to make it compile.
+        JavaSuspendWrapper.wrapSuspend<T>(continuation, it, answer) as T?
+    }
+}

mockito-kotlin/src/main/kotlin/com/nhaarman/mockitokotlin2/internal/KotlinSuspendWrapper.kt

@@ -0,0 +1,41 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2018 Niek Haarman
+ * Copyright (c) 2007 Mockito contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.nhaarman.mockitokotlin2.internal
+
+import org.mockito.invocation.InvocationOnMock
+import kotlin.coroutines.Continuation
+import kotlin.coroutines.suspendCoroutine
+
+suspend fun <T> wrapSuspend(
+    body: Function2<InvocationOnMock, Continuation<T>, T>,
+    invocationOnMock: InvocationOnMock
+): T {
+    //suspendCoroutine is needed to create new continuation.
+    return suspendCoroutine { continuation ->
+        //body is suspend lambda. From Java we got is as regular function so we could simple call it by providing own Continuation
+        body(invocationOnMock, continuation)
+    }
+}

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

@@ -8,6 +8,7 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.withContext
+import org.junit.Assert.assertEquals
 import org.junit.Test
 
 
@@ -157,11 +158,34 @@ class CoroutinesTest {
             verify(testSubject).suspending()
         }
     }
+
+    @Test
+    fun answerWithSuspendFunction() = runBlocking {
+        val fixture: SomeInterface = mock()
+
+        whenever(fixture.suspendingWithArg(any())).willAnswer {
+            withContext(Dispatchers.Default) { it.getArgument<Int>(0) }
+        }
+
+        assertEquals(5, fixture.suspendingWithArg(5))
+    }
+
+    @Test
+    fun inplaceAnswerWithSuspendFunction() = runBlocking {
+        val fixture: SomeInterface = mock {
+            onBlocking { suspendingWithArg(any()) } willAnswer {
+                withContext(Dispatchers.Default) { it.getArgument<Int>(0) }
+            }
+        }
+
+        assertEquals(5, fixture.suspendingWithArg(5))
+    }
 }
 
 interface SomeInterface {
 
     suspend fun suspending(): Int
+    suspend fun suspendingWithArg(arg: Int): Int
     fun nonsuspending(): Int
 }