Mockito Cheatsheet

As a Java developer, Mockito is your good friend for unit test. Using this to record some frequently used Mockito usages:

Verify if a method is called or not called.

Mockito.verify(mockObject, times(5)).mockMethodToVerify(); // verify a method is called 5 times.
Mockito.verify(mockObject, never()).mockMethodToVerify(); // verify a method is never called.

Control the behavior of a mocked method based on the passed in parameters

when(someMock.someMethod()).thenAnswer(new Answer() {
    private int count = 0;
    public Object answer(InvocationOnMock invocation) {
        if (count++ == 1)
            return 1;
        return 2;
    }
});

Use captor to capture function arguments

ArgumentCaptor<HashSet> captor = ArgumentCaptor.forClass(HashSet.class);
verify(obj).update(anyString(), captor.capture());
assertEquals("the captured HashSet should be empty.", 0, captor.getValue().size());

Use answer to return the parameter passed into a method.

when(mock.someMethod(anyString())).thenAnswer(invocation -> invocation.getArguments()[0]);

Or more simpler, using the built-in method by Mockito - AdditionalAnswers.

  when(mock.someMetod(anyString(), anyString()))
      .thenAnswer(AdditionalAnswers.returnsFirstArg());
  when(mock.someMetod(anyString(), anyString()))
      .thenAnswer(AdditionalAnswers.returnsSecondArg());
  when(mock.someMetod(anyString(), anyString()))
      .thenAnswer(AdditionalAnswers.returnsArgAt(2));