如何使用Mockito模拟方法调用

Question

i am trying to write Unittests for a MAS. Therefore i have to mock the agent an agent is communicating with. Here is an example of what i am trying to do at the moment. I have an agent A which is the one that i want to test. He calls B.method(arg) on an other agent B, which is mocked in my case. Normally B would call A.method(arg1, arg2, arg3). I am new to Mockito and doesn't know a lot about its possibilities. Is it possible to do something like when(mock.method).thenCall(A.method)?

Thanks for your help!

Answer 1

A little late to the party, but I believe would be able to achieve what you wanted with an Answer.

The following will call a real method (methodOnA), whenever the mock method (methodOnB) is called:

doAnswer(new Answer<Void>() {
    @Override
    public Void answer(InvocationOnMock invocationOnMock) throws Throwable {
        realObjectA.methodOnA()
        return null;
    }
}).when(mockObjectB).methodOnB();

Answer 2

The intent of mocking a method call is to immediately return a value (or throw an exception) when the method is called on the mock instance. It allows you to exercise the class-under-test without calling upon that class' collaborators.

So rather than delegate the method call to another method call, you would usually just thenResult(someValue) or thenThrow(someException) .

It may be that your test relies on a helper method to derive someValue , but that's unlikely to be a useful test.

Answer 3

You shouldn't do it, it's a bad design to ENFORCE B to call A (It is fine to do it, but enforcing it is wrong), the fact that B is calling A should be tested in B 's unitests, not A 's, and A should be unaware of it.

You can on the other hand, verify with Mockito that B.method() was invoked (and how many times, and with which argument), or alternatively return a stub value from B.method() without invoking A , which is a good unitest - since it checks for a single behavior of A . (The call to A.method() should be tested seperately).

For example, returning a stub value with Mockito is easily done with

Mockito.when(mockedB.method(SOME_ARG_HERE)).thenReturn(SOME_RESULT);

Much more useful examples and information can be found at Mockito's javadocs