Mocks allow us to write fast tests that don't mess with production data. Without OCMock we will need to write our own mocks, but it doesn't have to be a lot of work. We will look at techniques for practical mocking in Swift that will allow us to create simple, easy to maintain mocks for the most important parts of our codebase. Presented on March 4th, 2016 at try! Swift in Tokyo.

1. Good morning!

2. RealWorld Mocking
In Swift

3. YouWantToWriteTests

4. ButYou Don’tWantThem
To Mess UpYour
Real Stuff

5. Or Be Slow

6. let session = NSURLSession()
let url = NSURL(string: "http://www.tryswiftconf.com")!
let task = session.dataTaskWithURL(url) { (data, _, _) -> Void in
if let data = data {
let string = String(data: data, encoding: NSUTF8StringEncoding)
print(string)
}
}
task.resume()

7. OCMock can'tsave
you now

8. class HTTPClientTests: XCTestCase {
var subject: HTTPClient!
let session = MockURLSession()
override func setUp() {
super.setUp()
subject = HTTPClient(session: session)
}

9. class HTTPClientTests: XCTestCase {
var subject: HTTPClient!
let session = MockURLSession()
override func setUp() {
super.setUp()
subject = HTTPClient(session: session)
}
func test_GET_RequestsTheURL() {
let url = NSURL(string: "http://www.tryswiftconf.com")!
subject.get(url) { (_, _) -> Void in }

10. class HTTPClientTests: XCTestCase {
var subject: HTTPClient!
let session = MockURLSession()
override func setUp() {
super.setUp()
subject = HTTPClient(session: session)
}
func test_GET_RequestsTheURL() {
let url = NSURL(string: "http://www.tryswiftconf.com")!
subject.get(url) { (_, _) -> Void in }
XCTAssert(session.lastURL === url)
}
}

12. ItWillTakeALot Of
Time

13. YouWillWonder IfIt’s
Worth It

15. WhyUse Mocks» Make tests faster (like 1000s of times faster!) !
» Increase coverage of test suite "
» Make tests more robust #

16. Testing

18. TheTimeToWriteTests Is

19. Now

22. Dependency
Injection

23. class VideoCaptureManager: NSObject {
var userDefaults: UserDefaultsProtocol
//MARK: - Initializers
override init() {
self.userDefaults = UserDefaults()
}
convenience init(userDefaults: UserDefaultsProtocol) {
self.init()
self.userDefaults = userDefaults
}
}

24. “Dependency
injection means
givingan objectits
instancevariables.
Really.That's it.”
James Shore

25. WhyNotJustUseA
Singleton?

26. class VideoUploadManager {
static let sharedInstance = VideoUploadManager()
}
class TimeMachineAPI {
func uploadVideo(videoRecording: VideoRecording) {
VideoUploadManager.sharedInstance.upload(videoRecording: self.videoRecording, completion: { (error) -> Void in
if let error = error {
Log.error(error.localizedDescription)
}
})
}
}

27. Why Use DependencyInjection
» Easy customization !
» Clear ownership "
» Testability #

28. Constructor injection

29. Test Doubles

30. Types ofTestDoubles
» Stubs !
» Mocks "
» Partial mocks #

31. Stubs

32. “Fakesaresponseto
method calls ofan
object”
Unit Testing Tutorial: Mocking Objects

33. class StubTimeMachineAPI: TimeMachineAPI {
var videoUrl = "https://www.youtube.com/watch?v=SQ8aRKG9660"
func getVideoFor(year: Int) -> String {
return videoUrl
}
}

34. Mocks

35. “Letyou check ifa
method callis
performed or ifa
propertyis set”
Unit Testing Tutorial: Mocking Objects

36. class MockTimeMachine: TimeMachine {
var timeTravelWasCalled = false
mutating func timeTravelTo(year: Int) {
timeTravelWasCalled = true
}
}

37. Partial
Mock

38. “Anyactualobject
which has been
wrapped or
changed ”
Justin Searls

39. “to provide
artificial
responsesto some
methods butnot
others”
Justin Searls

40. PartialMocksAreAn
Anti-pattern

41. What’sWrongWith Partial Mocks?
» Challenging to set up !
» Decreases the comprehensibility of the test "

42. What’s Real?
What’s Fake?

43. Mocking

45. Mocking In Swift
ViaProtocols

46. “This kind oftesting
is reallysimilarto
whatyou getwith
mocks, butit’s so
much better.”
Protocol-Oriented Programming in Swift

47. “Mocksare
inherentlyfragile. ”
Protocol-Oriented Programming in Swift

48. “You haveto couple
yourtesting code”
Protocol-Oriented Programming in Swift

49. “tothe
implementation
details ofthe code
undertest.”
Protocol-Oriented Programming in Swift

50. PlaysWell
With Structs
And Classes

51. Protocols Help
WhenThere’s
InternalDependencies

53. They Said
Don’tMockTypes
You Don’tOwn

55. WhyIt’s BadTo MockTypesYou Don’tOwn
» Have to be sure that the behavior you implement in
a mock matches the external library
» The external library could change, breaking your
mock

56. MockingApple Framework Classes
class UserDefaultsMock: UserDefaultsProtocol {
private var objectData = [String : AnyObject]()
func objectForKey(key: UserDefaultsKey) -> AnyObject? {
return objectData[key.name]
}
func setObject(value: AnyObject?, forKey key: UserDefaultsKey) {
objectData[key.name] = value
}
func removeObjectForKey(key: UserDefaultsKey) {
objectData[key.name] = nil
}
}

57. Time Traveler
Times

58. TestThatUses UserDefaultsMock
func testNotificationSettingsLoad() {
let userDefaultsMock = UserDefaultsMock()
mockUserDefaults.setObject("NEVER", forKey: "timeMachineBreakingNewsPushNotification")
mockUserDefaults.setObject("NEVER", forKey: "timeMachineDailyDigestPushNotification")
let dataProvider = PushNotificationsDataProvider(userDefaults: mockUserDefaults)
let expectedFrequencies: [PushNotificationFrequency] = [.Never, .All, .All, .Never]
XCTAssertEqual(expectedFrequencies, dataProvider.notificationSettings.values)
}

59. Mocking NSNotificationCenterWas NotWorth It
» Complex !
» Injected throughout entire codebase "
» Limited functionality compared to real object #
» Solves a problem that doesn’t really exist $

60. TheySaid
Don’tMock
ValueTypes

61. “Whenyou’re
doing...simple data
inand dataout,you
don’tneed mocking
or stubbing. ”
Andy Matuschak

62. “You can passa
value intoa
function,then look
atthe resulting
value.”
Andy Matuschak

64. “Trymakingyour
referencetypes
immutable”
Joe Groff

66. WhatMakesaGood Mock
» Quick and easy to write
» Relatively short and does not contain tons of
information you don’t need
» Legitimate reason to not use real object

67. I amthoughtful
aboutwhat gets mocked
andwhy

68. Fellowtime
travelers

69. Let’s looktowards
the future

70. SwiftMocking Frameworks

71. Dobby
MockFive
SwiftMock

72. Cuckoo

73. AWorld
WithoutMocks

74. WrapUp
! If you want to improve your codebase, write tests
! Mocks allow you to write great tests
! Create simple mocks that will last

75. Write Mocks
And UseThem
For Great Good

76. ! " !