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Good morning!
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Real World Mocking
In Swift
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You Want To Write Tests
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But You Don’t Want Them
To Mess Up Your
Real Stuff
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Or Be Slow
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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()
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OCMock can't save
you now
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class HTTPClientTests: XCTestCase {
var subject: HTTPClient!
let session = MockURLSession()
override func setUp() {
super.setUp()
subject = HTTPClient(session: session)
}
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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 }
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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)
}
}
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It Will Take A Lot Of
Time
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You Will Wonder If It’s
Worth It
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Why Use Mocks
» Make tests faster (like 1000s of times faster!) !
» Increase coverage of test suite "
» Make tests more robust #
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Testing
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The Time
To Write Tests Is
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Now
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Dependency
Injection
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class VideoCaptureManager: NSObject {
var userDefaults: UserDefaultsProtocol
//MARK: - Initializers
override init() {
self.userDefaults = UserDefaults()
}
convenience init(userDefaults: UserDefaultsProtocol) {
self.init()
self.userDefaults = userDefaults
}
}
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“Dependency
injection means
giving an object its
instance variables.
Really. That's it.”
James Shore
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Why Not Just Use A
Singleton?
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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)
}
})
}
}
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Why Use Dependency Injection
» Easy customization !
» Clear ownership "
» Testability #
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Constructor injection
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Test Doubles
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Types of Test Doubles
» Stubs !
» Mocks "
» Partial mocks #
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Stubs
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“Fakes a response to
method calls of an
object”
Unit Testing Tutorial: Mocking Objects
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class StubTimeMachineAPI: TimeMachineAPI {
var videoUrl = "https://www.youtube.com/watch?v=SQ8aRKG9660"
func getVideoFor(year: Int) -> String {
return videoUrl
}
}
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Mocks
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“Let you check if a
method call is
performed or if a
property is set”
Unit Testing Tutorial: Mocking Objects
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class MockTimeMachine: TimeMachine {
var timeTravelWasCalled = false
mutating func timeTravelTo(year: Int) {
timeTravelWasCalled = true
}
}
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Partial
Mock
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“Any actual object
which has been
wrapped or
changed ”
Justin Searls
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“to provide
artificial
responses to some
methods but not
others”
Justin Searls
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Partial Mocks Are An
Anti-pattern
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What’s Wrong With Partial Mocks?
» Challenging to set up !
» Decreases the comprehensibility of the test "
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What’s Real?
What’s Fake?
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Mocking
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Mocking In Swift
Via Protocols
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“This kind of testing
is really similar to
what you get with
mocks, but it’s so
much better.”
Protocol-Oriented Programming in Swift
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“Mocks are
inherently fragile. ”
Protocol-Oriented Programming in Swift
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“You have to couple
your testing code”
Protocol-Oriented Programming in Swift
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“to the
implementation
details of the code
under test.”
Protocol-Oriented Programming in Swift
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Plays Well
With Structs
And Classes
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Protocols Help
When There’s
Internal Dependencies
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They Said
Don’t Mock Types
You Don’t Own
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Why It’s Bad To Mock Types You Don’t Own
» Have to be sure that the behavior you implement in
a mock matches the external library
» The external library could change, breaking your
mock
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Mocking Apple 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
}
}
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Time Traveler
Times
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Test That Uses 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)
}
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Mocking NSNotificationCenter Was Not Worth It
» Complex !
» Injected throughout entire codebase "
» Limited functionality compared to real object #
» Solves a problem that doesn’t really exist $
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They Said
Don’t Mock
Value Types
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“When you’re
doing...simple data
in and data out, you
don’t need mocking
or stubbing. ”
Andy Matuschak
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“You can pass a
value into a
function, then look
at the resulting
value.”
Andy Matuschak
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“Try making your
reference types
immutable”
Joe Groff
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What Makes a Good 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
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I am thoughtful
about what gets mocked
and why
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Fellow time
travelers
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Let’s look towards
the future
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Swift
Mocking Frameworks
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Dobby
MockFive
SwiftMock
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Cuckoo
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A World
Without Mocks
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Wrap Up
! If you want to improve your codebase, write tests
! Mocks allow you to write great tests
! Create simple mocks that will last
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Write Mocks
And Use Them
For Great Good
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! " !