Better Design Through Testing

Transcript

1. Better design through testing: With OCUnit, OCMock Cofounder of Waveface Inc. Jamie Sa @jamex
2. Bike Messenger
3. What is a good design?
4. Agile is good™
5. 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
6. 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
7. 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
8. 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
9. 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
10. Testing makes it feels nature
11. An example View Controller Model
12. An example View Controller Model Network
13. An example View Controller Model Network
14. An example View Controller Model Network What should we do with this?
15. Mock is here to save you
16. Mocks are pre-programmed with expectations which form a speci cation of the calls they are expected to receive. - Gerard Meszaros (XUnit Test Patterns)
17. 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
18. 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.
19. Method Swizzling #import <objc/runtime.h> @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
20. Method Swizzling is •not Mock •less messy (in terms of testing) • only effect current runtime •Could be tedious •Still just a Stub
21. OCMock #import <OCMock/OCMock.h> @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
22. 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)
23. With OCHamcrest #define HC_SHORTHAND #import <OCHamcrest/OCHamcrest.h> @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
24. 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
25. References •LinkedImageFetcher by Quinn “The Eskimo!” •The Pragmatic Programmer by Andrew Hunt, David Thomas •Intro to Objective-C TDD by Jon Reid