Question

Mockito seems like a pretty sweet stubbing/mocking framework for Java. The only problem is I can’t find any concrete documentation on the best ways of using their API. Common methods used in tests include:

doXXX(???) : Stubber
when(T) : OngoingStubbing
then(T) : OngoingStubbing
verify(???) : T
given(T) : BDDOngoingStubbing
willXXX(???) : BDDStubber

When you see examples of Mockito in practice, you see code like:

when(yourMethod()).thenReturn(5);

From all the docs I’ve read, I’ve identified several "patterns" of Mockito "grammars" obtained from daisy-chaining these method calls together like the example above. Some common patterns I’ve found are:

When/Then: when(yourMethod()).thenReturn(5);

Given/Will: given(yourMethod()).willThrow(OutOfMemoryException.class);

Do/When: doReturn(7).when(yourMock.fizzBuzz());

Will/Given/Do: willReturn(any()).given(yourMethod()).doNothing();

Verify/Do: verify(yourMethod()).doThrow(SomeException.class);

What I’m choking on is how to select the right pattern/combination of method calls to model my test cases. It seems like you can daisy-chain these together in seemingly endless combos and I’m not sure what pattern is right for which problem.

Can some Mockito Guru help shed some light as to which patterns/combinations of Mockito methods are used for which types of test cases (and why)? Thanks in advance!

Answer 1

Mockito often have several ways of doing things.

I find myself using mostly:

// Setup expectations
when(object.method()).thenReturn(value);
when(object.method()).thenThrow(exception);
doThrow(exception).when(object.voidMethod());


// verify things
verify(object, times(2)).method();
verify(object, times(1)).voidMethod();

I’ve found that i can do 95% of what i need to with these three kinds of calls.

Also, what version of Mockito are you using? “given” and “will” constructs are not present in the latest version (1.9.0+)

However, there are cases where I want the return value or exception to respond to the input. In this case, you can use the Answer interface to inspect the method arguments and return an appropriate value.

public class ReturnFirstArg<T> implements Answer<T> {
    public T answer(InvocationOnMock invocation) {
        return invocation.getArguments()[0];
    }
}

when(object.method(7)).thenAnswer(new ReturnFirstArg<Integer>());