CODEWITHSUNDEEP
javamockito
sprinter
sprinter

Reputation: 27946

Using a `when` as verification

I have a utility method used in hundreds of tests to mock the return value from a customised randomiser. Here's a (highly artificial) model of my code:

interface CardRandomiser{
    Card getCard(Suit suit);
}

void mockCard(Suit suit, Face face) {
    CardRandomiser rand = mock(CardRandomiser.class);
    when(rand.getCard(suit)).thenReturn(new Card(suit, face));
    Game.setCardRandomiser(rand);
}

This can then be used as:

mockCard(Suit.CLUBS, Face.QUEEN);
Card card = pickACardAnyCard();
assertThat(card.getFace(), is(Face.QUEEN));

However this makes some bugs a bit hard to pick up. If the method under test incorrectly asks for Suit.HEARTS then the mock returns null and the assertion correctly fails. But it's impossible to tell through the error message what was passed to the mock.

Clearly I could handle this with a verify. I could pass the mock back out of mockCard function and then separately verify that is was called with the correct value. But that really clutters up the tests assertions that are not really related to what's being tested. Given every time this method is called I am specifying an expected argument value I'd prefer to put the assertion in one place. Note that this all occurs before the method under test is called.

Ideally I'd like the when statement to throw an exception if it's called with an unexpected value. Something like:

when(rand.getCard(suit)).thenReturn(new Card(suit, face));
when(rand.getCard(intThat(not(is(suit))))).thenThrow(new IllegalArgumentException());

This works and stops the test when getCard is called which is better. But it still doesn't allow me to show what the incorrect argument was.

I also tried it using an ArgumentCaptor and then checking the captured value. But it's clear they are for verify statements rather than when statements.

Is there a standard Mockito way of doing this, or do I need to clutter my tests with verify statements?

Upvotes: 0

Views: 56

Answers (1)

Evgeny
Evgeny

Reputation: 2568

You can configure mockito answer using thenAnswer, e.g.

private CardRandomiser mockCard(final Suit suit, final Face face) {
    CardRandomiser rand = mock(CardRandomiser.class);

    when(rand.getCard(any(Suit.class))).thenAnswer(new Answer<Card>() {
        @Override
        public Card answer(InvocationOnMock invocation) throws Throwable {
            if(!suit.equals(invocation.getArguments()[0])) {
                 throw new IllegalArgumentException(
                         String.format("Value %s passed, but mocked for %s", invocation.getArguments()[0], suit));
            }
            return new Card(suit, face);
        }
    });

    return rand;
}

Upvotes: 2

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