org.mockito.exceptions.misusing.MissingMethodInvocationException in MOCKITO

The problem:

Below is your test class

class ControllerTest{ @Autowired lateinit var myIntF: MyInterface @Test fun controllerTest(){ Mockito.`when`(myIntF.getmyStringData()).thenReturn("Some mock string") // Some code over here } 

Since you have used @Autowired, the real implementation is used and not the mock object and hence when you do Mockito.when(myIntF.getmyStringData()).thenReturn("Some mock string") , you get the error when() requires an argument which has to be 'a method call on a mock'. This is because myIntF is not a mock object.

The solution:

First, since it's a controller test, you need to have the controller field annotated with @InjectMocks to inject the mocked MyInterface obj into it. Then you need to annotate the MyInterface field with @Mock which would create a mocked object. Then you need to have a @Before or @BeforeEach method with MockitoAnnotations.initMocks(this) to initialize objects annotated with Mockito annotations. Only after that, the method call mocking with Mockito.when(mockedObject.methodCall).thenReturn(mockedValue) would work.

class ControllerTest{ @InjectMocks lateinit var controller: MyController @Mock lateinit var myIntF: MyInterface @BeforeEach fun init() { MockitoAnnotations.initMocks(this) } @Test fun controllerTest(){ Mockito.`when`(myIntF.getmyStringData()).thenReturn("Some mock string") // Some code over here controller.callFx() //this would return "Some mock string" } 

I'm not familiar with @Autowire so this might be a completely wrong assumption, but it's also too big for a comment, so here it goes.

The exception basically explains that the object you're trying to mock isn't a mock and from what I can see, this is true.

Usually one can do something like:

@Mock lateinit var myIntF: Myinterface @Before fun setUp() { MockitoAnnotations.initMocks(this) } 

And now the mock is created and you can configure it with when like you have.

There are other options to initialize this, such as running the test with the mockito test runner. I believe there's also a test rule and you'll always have mockito-kotlin which is great for kotlin code and it's much simpler in my personal opinion:

lateinit var myIntF = mock<Myinterface>() @Test fun controllerTest(){ myIntF.stub { on { getmyStringData() } doReturn "Some mock string" } } 

The point here is that I think you didn't actually create a mock and mockito needs this because if I'm not mistaken it works by inheriting from the class it's mocking.

Edit:

As pointed out in the comments you might want to test the controller. This means you'll need to instantiate it with the mocks you've created. One suggested way is to use @InjectMocks. Something like:

@InjectMocks lateinit var controller: MyController 

But without knowing the whole test code it's hard to say this is exactly what you want.