I have a following test method:
MyClass myClass= Mockito.mock(MyClass.class); Mockito.when(myClass.methodUsedInMethodBeingTested(Matchers.any(MyTypeParam.class))
You are invoking the methodToTest on the mock instance. Because you have not configured it otherwise, that just returns null, it doesn't try to invoke any of the actual method's implementation.
methodToTest