Using Multiple ArgumentMatchers on the same mock

Question

I am trying to do this using Mockito on a Mock:
When Mock.someMethod(..) is called with argument1 --> return result1
When Mock.someMethod(..) is called with argument2 --> return result2
When Mock.someMethod(..) is called with argument3 --> return result3

    when(mock.method(Matchers.argThat(new MyMatcher1() {

        @Override
        public boolean matches(Object arg0) {
                   // comparision logic
        }
    }))).thenReturn(result1);

    when(mock.method(Matchers.argThat(new MyMatcher2() {

        @Override
        public boolean matches(Object arg0) {
                   // comparision logic
        }
    }))).thenReturn(result2);

    when(mock.method(Matchers.argThat(new MyMatcher3() {

        @Override
        public boolean matches(Object arg0) {
                   // comparision logic
        }
    }))).thenReturn(result3);

But Mockito stubs the first one correctly, but on the second one it throws NullPointer exception as it for some reason tries to run the Matcher with null agrument. I am not sure if it is supported.

If this is not the correct way, how to achieve this with Mockito? Thanks.

Answer 1

Instead of writing

when(mock.method(Matchers.argThat(new MyMatcher1() {
    @Override
    public boolean matches(Object arg0) {
           // comparison logic
    }
}))).thenReturn(result1);

Try this.

doReturn(result1).when(mock).method(Matchers.argThat(new MyMatcher1() {

    @Override
    public boolean matches(Object arg0) {
               // comparison logic
    }
}));

and similarly for result2 and result3.

This is described at http://docs.mockito.googlecode.com/hg/latest/org/mockito/Mockito.html#12, but in my opinion, the documentation is unclear about the fact that this construction is actually needed in this case. I will talk to the rest of the Mockito team about improving the documentation here.

Good luck.

Answer 2

As a rule of thumb, if a test fails, you should be able to pinpoint what is wrong with the unit under test. Avoid writing custom matchers specifically for one test. If a method needs to return more than one value, it is usually sufficient to simply stub the method by returning the values in the order the test predicts.

e.g.

when(mock.method(any(Object.class))).thenReturn(result1, result2, result3);

This will return result 1 one the first invocation, result2 on the second and so on.

There are obviously scenarios where this is insufficient, but more often than not, the simpler test is the better one.