Example of mocking.

DeckTest.m

- (void)testShouldKnowCardsCanBeAddedToDeck {
    Deck *deck = [Deck new];
    Card *card = [[Card alloc] initWithContents:@"Test Card"];

    id cardsMock = [OCMockObject mockForClass:[NSMutableArray class]];
    [[cardsMock expect] addObject:card];

    deck.cards = cardsMock;
    [deck addCard:card atTop:NO];

    [cardsMock verify];
}

- (void)testShouldKnowCardsCanBeAddedToTopOfDeck {
    Deck *deck = [Deck new];
    Card *card = [[Card alloc] initWithContents:@"Test Card"];

    id cardsMock = [OCMockObject mockForClass:[NSMutableArray class]];
    [[cardsMock expect] insertObject:card atIndex:0];

    deck.cards = cardsMock;
    [deck addCard:card atTop:YES];

    [cardsMock verify];
}