Stubbing a method that takes Class<T> as parameter with Mockito

Question

There is a generic method that takes a class as parameter and I have problems stubbing it with Mockito. The method looks like this:

public <U extends Enum<U> & Error, T extends ServiceResponse<U>> T validate(     Object target, Validator validator, Class<T> responseClass,     Class<U> errorEnum); 

It's god awful, at least to me... I could imagine living without it, but the rest of the code base happily uses it...

I was going to, in my unit test, stub this method to return a new empty object. But how do I do this with mockito? I tried:

when(serviceValidatorStub.validate(     any(),      isA(UserCommentRequestValidator.class),      UserCommentResponse.class,      UserCommentError.class) ).thenReturn(new UserCommentResponse()); 

but since I am mixing and matching matchers and raw values, I get "org.mockito.exceptions.misusing.InvalidUseOfMatchersException: Invalid use of argument matchers!"

Answer 1

The problem is, you cannot mix argument matchers and real arguments in a mocked call. So, rather do this:

when(serviceValidatorStub.validate(     any(),     isA(UserCommentRequestValidator.class),     eq(UserCommentResponse.class),     eq(UserCommentError.class)) ).thenReturn(new UserCommentResponse()); 

Notice the use of the eq() argument matcher for matching equality.

see: https://static.javadoc.io/org.mockito/mockito-core/1.10.19/org/mockito/Matchers.html#eq(T)

Also, you could use the same() argument matcher for Class<?> types - this matches same identity, like the == Java operator.

Answer 2

Just in order to complete on the same thread, if someone want to stubb a method that takes a Class as argument, but don't care of the type, or need many type to be stubbed the same way, here is another solution:

private class AnyClassMatcher extends ArgumentMatcher<Class<?>> {      @Override     public boolean matches(final Object argument) {         // We always return true, because we want to acknowledge all class types         return true;     }  }  private Class<?> anyClass() {     return Mockito.argThat(new AnyClassMatcher()); } 

and then call

Mockito.when(mock.doIt(this.anyClass())).thenCallRealMethod();