Mockito match specific Class argument

Question

I am trying to mock some resources that are generated dynamically. In order to generate these resources, we must pass in a class argument. So for example:

FirstResourceClass firstResource = ResourceFactory.create(FirstResourceClass.class);

SecondResourceClass secondResource = ResourceFactory.create(SecondResource.class);

This is well and good until I tried to mock. I am doing something like this:

PowerMockito.mockStatic(ResourceFactory.class);
FirstResourceClass mockFirstResource = Mockito.mock(FirstResourceClass.class);
SecondResourceClass mockSecondResource = Mockito.mock(SecondResourceClass.class);

PowerMockito.when(ResourceFactory.create(Matchers.<Class<FirstResourceClass>>any()).thenReturn(mockFirstResource);
PowerMockito.when(ResourceFactory.create(Matchers.<Class<SecondResourceClass>>any()).thenReturn(mockSecondResource);

It seems like the mock is being injected into the calling class, but FirstResourceClass is being send mockSecondResource , which throws a compile error.

The issue is (I think) with the use of any() (which I got from this question ). I believe I have to use isA() , but I'm not sure how to make that method call, as it requires a Class argument. I have tried FirstResourceClass.class , and that gives a compile error.

Answer 1

You want eq , as in:

PowerMockito.when(ResourceFactory.create(Matchers.eq(FirstResourceClass.class)))
    .thenReturn(mockFirstResource);

any() ignores the argument, and isA will check that your argument is of a certain class—but not that it equals a class, just that it is an instanceof a certain class. ( any(Class) has any() semantics in Mockito 1.x and isA semantics in 2.x.)

isA(Class.class) is less specific than you need to differentiate your calls, so eq it is. Class objects have well-defined equality, anyway, so this is easy and natural for your use-case.

Because eq is the default if you don't use matchers, this also works:

PowerMockito.when(ResourceFactory.create(FirstResourceClass.class))
    .thenReturn(mockFirstResource);

Note that newer versions of Mockito have deprecated the Matchers name in favor of ArgumentMatchers, and Mockito.eq also works (albeit clumsily, because they're "inherited" static methods).