Card equals tests and evolving implementations

gistfile1.m

// FIRST TEST
- (void)testShouldKnowCardsWithSameContentsAreEqual {
    Card *card = [[Card alloc] initWithContents:@"Test Card"];
    Card *equalCard = [[Card alloc] initWithContents:@"Test Card"];

    STAssertEqualObjects(card, equalCard, @"Cards with the same content should be equal");
}
// RED isEqual is not yet overriden
// GREEN returns YES
- (BOOL)isEqual:(id)other {
    return YES;
}


// SECOND TEST
- (void)testShouldKnowCardCannotBeEqualToADifferentObject {
    Card *card = [[Card alloc] initWithContents:@"Test Card"];
    STAssertFalse([card isEqual:@"Not a Card"], @"Cards with the same content should be equal");
}
// RED isEqual always returns YES
// GREEN isEqual checks type and returns NO
- (BOOL)isEqual:(id)other {
    if (![[other class] isEqual:[self class]])
        return NO;
    return YES;
}


// THIRD TEST
- (void)testShouldKnowCardsWithDifferContentsAreNotEqual {
    Card *card = [[Card alloc] initWithContents:@"Test Card"];
    Card *differentCard = [[Card alloc] initWithContents:@"Different Test Card"];

    STAssertFalse([card isEqual: differentCard], @"Cards with the different content should not be equal");
}
// RED always returns YES if other is a card
// GREEN delegates isEqual to NSString *contents
- (BOOL)isEqual:(id)other {
    if (![[other class] isEqual:[self class]])
        return NO;
    return [self.contents isEqualToString:((Card *)other).contents];
}


// FORTH TEST - Hash needs to be overriden too
- (void)testShouldKnowCardHashEqualsContentsHash {
    Card *card = [[Card alloc] initWithContents:@"Test Card"];
    STAssertEquals([card hash], [card.contents hash] , @"Card hash must equal its contents hash");
}
// RED hash is not yet overriden
// GREEN delegate to NSString *contents
- (NSUInteger)hash {
    return [self.contents hash];
}