kotlin and ArgumentCaptor - IllegalStateException

Question

I have a problem with capturing the Class argument via ArgumentCaptor. My test class looks like this:

@RunWith(RobolectricGradleTestRunner::class) @Config(sdk = intArrayOf(21), constants = BuildConfig::class) class MyViewModelTest {     @Mock     lateinit var activityHandlerMock: IActivityHandler;      @Captor     lateinit var classCaptor: ArgumentCaptor<Class<BaseActivity>>      @Captor     lateinit var booleanCaptor: ArgumentCaptor<Boolean>      private var objectUnderTest: MyViewModel? = null      @Before     fun setUp() {         initMocks(this)         ...         objectUnderTest = MyViewModel(...)     }      @Test     fun thatNavigatesToAddListScreenOnAddClicked(){         //given          //when         objectUnderTest?.addNewList()          //then         verify(activityHandlerMock).navigateTo(classCaptor.capture(), booleanCaptor.capture())         var clazz = classCaptor.value         assertNotNull(clazz);         assertFalse(booleanCaptor.value);     } } 

When I run the test, following exception is thrown:
java.lang.IllegalStateException: classCaptor.capture() must not be null
Is it possible to use argument captors in kotlin?

========= UPDATE 1:
Kotlin: 1.0.0-beta-4584
Mockito: 1.10.19
Robolectric: 3.0

========= UPDATE 2:
Stacktrace:

java.lang.IllegalStateException: classCaptor.capture() must not be null  at com.example.view.model.ShoplistsViewModelTest.thatNavigatesToAddListScreenOnAddClicked(ShoplistsViewModelTest.kt:92) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.robolectric.RobolectricTestRunner$2.evaluate(RobolectricTestRunner.java:251) at org.robolectric.RobolectricTestRunner.runChild(RobolectricTestRunner.java:188) at org.robolectric.RobolectricTestRunner.runChild(RobolectricTestRunner.java:54) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.robolectric.RobolectricTestRunner$1.evaluate(RobolectricTestRunner.java:152) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144) 

Answer 1

From this blog

"Getting matchers to work with Kotlin can be a problem. If you have a method written in kotlin that does not take a nullable parameter then we cannot match with it using Mockito.any(). This is because it can return void and this is not assignable to a non-nullable parameter. If the method being matched is written in Java then I think that it will work as all Java objects are implicitly nullable."

A wrapper function is needed that returns ArgumentCaptor.capture() as nullable type.

Add the following as a helper method to your test

fun <T> capture(argumentCaptor: ArgumentCaptor<T>): T = argumentCaptor.capture() 

Please see, MockitoKotlinHelpers.kt provided by Google in the Android Architecture repo for reference. the capture function provides a convenient way to call ArgumentCaptor.capture(). Call

verify(activityHandlerMock).navigateTo(capture(classCaptor), capture(booleanCaptor)) 

Update: If the above solution does not work for you, please check Roberto Leinardi's solution in the comments below.

Answer 2

The return value of classCaptor.capture() is null, but the signature of IActivityHandler#navigateTo(Class, Boolean) does not allow a null argument.

The mockito-kotlin library provides supporting functions to solve this problem.

Code should be:

    @Captor     lateinit var classCaptor: ArgumentCaptor<Class<BaseActivity>>      @Captor     lateinit var booleanCaptor: ArgumentCaptor<Boolean>      ...      @Test     fun thatNavigatesToAddListScreenOnAddClicked(){         //given          //when         objectUnderTest?.addNewList()          //then         verify(activityHandlerMock).navigateTo( com.nhaarman.mockitokotlin2.capture<Class<BaseActivity>>(classCaptor.capture()),  com.nhaarman.mockitokotlin2.capture<Boolean>(booleanCaptor.capture()) )         var clazzValue = classCaptor.value         assertNotNull(clazzValue);         val booleanValue = booleanCaptor.value         assertFalse(booleanValue);     } 

OR

var classCaptor = com.nhaarman.mockitokotlin2.argumentCaptor<Class<BaseActivity>>() var booleanCaptor = com.nhaarman.mockitokotlin2.argumentCaptor<Boolean>() ...  verify(activityHandlerMock).navigateTo( classCaptor.capture(),  booleanCaptor.capture() ) 

also in build.gradle add this:

testImplementation "com.nhaarman.mockitokotlin2:mockito-kotlin:2.2.0"