Better design through testing: With OCUnit, OCMock Cofounder of Waveface Inc. Jamie Sa @jamex

Bike Messenger

What is a good design?

Agile is good™

Law of Demeter The Law of Demeter of functions states that any method of an object should call only methods belonging to: @interface Demeter : NSObject{ @private A *a; } - (void) example: (B *) b; @end @implementation Demeter - (NSUInteger)func { ... } - (void)example:(B *)b { C *c; [self func]; [b invert]; a = [[A alloc] init]; a.active = YES; [c print]; } @end

Law of Demeter The Law of Demeter of functions states that any method of an object should call only methods belonging to: @interface Demeter : NSObject{ @private A *a; } - (void) example: (B *) b; @end @implementation Demeter - (NSUInteger)func { ... } - (void)example:(B *)b { C *c; [self func]; [b invert]; a = [[A alloc] init]; a.active = YES; [c print]; } @end itself

Law of Demeter The Law of Demeter of functions states that any method of an object should call only methods belonging to: @interface Demeter : NSObject{ @private A *a; } - (void) example: (B *) b; @end @implementation Demeter - (NSUInteger)func { ... } - (void)example:(B *)b { C *c; [self func]; [b invert]; a = [[A alloc] init]; a.active = YES; [c print]; } @end itself any parameters that were passed in to the method

Law of Demeter The Law of Demeter of functions states that any method of an object should call only methods belonging to: @interface Demeter : NSObject{ @private A *a; } - (void) example: (B *) b; @end @implementation Demeter - (NSUInteger)func { ... } - (void)example:(B *)b { C *c; [self func]; [b invert]; a = [[A alloc] init]; a.active = YES; [c print]; } @end itself any parameters that were passed in to the method any object it created

Law of Demeter The Law of Demeter of functions states that any method of an object should call only methods belonging to: @interface Demeter : NSObject{ @private A *a; } - (void) example: (B *) b; @end @implementation Demeter - (NSUInteger)func { ... } - (void)example:(B *)b { C *c; [self func]; [b invert]; a = [[A alloc] init]; a.active = YES; [c print]; } @end itself any parameters that were passed in to the method any directly held component objects any object it created

Testing makes it feels nature

An example View Controller Model

An example View Controller Model Network

An example View Controller Model Network

An example View Controller Model Network What should we do with this?

Mock is here to save you

Mocks are pre-programmed with expectations which form a speci cation of the calls they are expected to receive. - Gerard Meszaros (XUnit Test Patterns)

Category @implementation NSUserDefaults (UnitTesting) -(id)valueForKey:(NSString *)key { return @"SetByCategory"; } @end @implementation CategoryTests - (void)testUserDefaultsSwitch { NSString * key = [[NSUserDefaults standardUserDefaults] valueForKey:@"aKey"]; STAssertEquals(key, @"SetByCategory", @"should be nil"); } @end

Category is •Not Mock • No expectation • Don’t form a spec •Make a mess •It’s just a Stub. • provides canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test.

Method Swizzling #import @interface MYNSUserDefaults : NSUserDefaults @end @implementation MYNSUserDefaults - (id)valueForKeySwizzled:(NSString *)key { return @"SetByMethodSwizzling"; } @end @implementation MethodSwizzlingTests - (void)testUserDefaultsSwitch { Method original = class_getInstanceMethod( [NSUserDefaults class], @selector(valueForKey:)); Method swizzled = class_getInstanceMethod( [MYNSUserDefaults class], @selector(valueForKeySwizzled:)); method_exchangeImplementations(original, swizzled); NSString * key = [[NSUserDefaults standardUserDefaults] valueForKey:@"aKey"]; STAssertEquals(key, @"SetByMethodSwizzling", @"should be nil"); } @end

Method Swizzling is •not Mock •less messy (in terms of testing) • only effect current runtime •Could be tedious •Still just a Stub

OCMock #import @implementation MockTests - (void) testMockUserDefaults { id mockUserDefaults = [OCMockObject mockForClass:[NSUserDefaults class]]; [[[mockUserDefaults expect] andReturn:@"aKeyFromMock"] valueForKey:@"aKey"]; NSString * key = [mockUserDefaults valueForKey:@"aKey"]; STAssertTrue([key isEqualToString:@"aKeyFromMock"], @"Mocking"); [mockUserDefaults verify]; } @end

OCMock is •a real Mock ✓ expect what to expect ✓ form a spec ✓ clean • Many other tricks can be done • Making async calls “sync” • Bypass expensive operations (NSURLConnection)

With OCHamcrest #define HC_SHORTHAND #import @implementation MockTests - (void) testMockUserDefaultsWithMatcher { id mockUserDefaults = [OCMockObject mockForClass:[NSUserDefaults class]]; [[[mockUserDefaults expect] andReturn:@"aKeyFromMock"] valueForKey:@"aKey"]; NSString * key = [mockUserDefaults valueForKey:@"aKey"]; assertThat(key, equalTo(@"aKeyFromMock")); [mockUserDefaults verify]; } @end

Common good practice •Put les in right target. Not too many, not to less. •Application testing and Unit Testing. •Expect to take 50+% more time with the same feature •Make it into Continuous Integration

References •LinkedImageFetcher by Quinn “The Eskimo!” •The Pragmatic Programmer by Andrew Hunt, David Thomas •Intro to Objective-C TDD by Jon Reid