In this talk I explain how you can use the Codable protocol to easily create mock json data for unit tests.

1. !

2. The Testing Games: Mocking, yay!
And may the mocks be ever in your favour

3. I like testing
It allows me to prove my code works

4. But I’m also quite lazy
And I know I’m not alone

5. Improving our own tests

6. Improving our own tests
1. Create a set of guidelines

7. Improving our own tests
1. Create a set of guidelines
2. Update the testing framework’s DSL (we use Quick)

8. Improving our own tests
1. Create a set of guidelines
2. Update the testing framework’s DSL (we use Quick)
3. Change the way we think about mocking

9. class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
}
}
}
}

10. class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
}
}
}
}
This isn’t too bad, right?

11. class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
let service = AuthenticationService(api: self)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == "Donny"
expect(user?.id) == 1
}
}
}
}
}
extension AuthenticationServiceTests: AuthenticationAPi {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let json = """
{"status": "ok", "user": {"id": 1, "name": “Donny"}}
""".data(using: .utf8)
callback(json, nil)
}
}

12. This is hard to read!
class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
let service = AuthenticationService(api: self)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == "Donny"
expect(user?.id) == 1
}
}
}
}
}
extension AuthenticationServiceTests: AuthenticationAPi {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let json = """
{"status": "ok", "user": {"id": 1, "name": “Donny"}}
""".data(using: .utf8)
callback(json, nil)
}
}

13. All values are hardcoded
class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
let service = AuthenticationService(api: self)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == "Donny"
expect(user?.id) == 1
}
}
}
}
}
extension AuthenticationServiceTests: AuthenticationAPi {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let json = """
{"status": "ok", "user": {"id": 1, "name": “Donny"}}
""".data(using: .utf8)
callback(json, nil)
}
}

14. The json is inline
class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
let service = AuthenticationService(api: self)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == "Donny"
expect(user?.id) == 1
}
}
}
}
}
extension AuthenticationServiceTests: AuthenticationAPi {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let json = """
{"status": "ok", "user": {"id": 1, "name": “Donny"}}
""".data(using: .utf8)
callback(json, nil)
}
}

16. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""

17. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""

18. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""

19. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""

20. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""

21. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""

22. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""
let serverError = """
{"status": "error", "code": 1004, "message": "Something went wrong on the server"}
"""

24. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""

25. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""

26. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""

27. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""

28. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""

29. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""

30. let passwordError = """
{"status": "error", "code": 1001, "message": "Wrong password"}
"""
let usernameError = """
{"status": "error", "code": 1002, "message": "User not found"}
"""
let validationError = """
{"status": "error", "code": 1003, "message": "Username or password missing"}
"""
let serverError = """
{"status": "error", "code": 1004, "message": "Something went wrong on the server"}
"""

31. let json = """
{
"_id": "5b05709156da3c5e1a933dce",
"index": 0,
"guid": "ca6507f6-f462-478e-ad4d-f9e46f9ee88a",
"isActive": true,
"balance": "$3,125.88",
"picture": "http://placehold.it/32x32",
"age": 38,
"eyeColor": "green",
"name": {
"first": "Dunlap",
"last": "Lott"
},
"company": "FUELTON",
"email": "dunlap.lott@fuelton.biz",
"phone": "+1 (888) 407-2414",
"address": "883 Nixon Court, Wolcott, Marshall Islands, 2469",
"about": "Dolor tempor ullamco deserunt tempor sunt esse irure ut fugiat. Irure occaecat fugiat deserunt
ad. Ipsum laborum excepteur excepteur dolore qui aliqua. Ad tempor culpa commodo laborum laboris ut
amet elit est cupidatat consectetur nostrud consequat.",
"registered": "Saturday, August 5, 2017 12:57 PM",

32. let json = """
{
"_id": "5b05709156da3c5e1a933dce",
"index": 0,
"guid": "ca6507f6-f462-478e-ad4d-f9e46f9ee88a",
"isActive": true,
"balance": "$3,125.88",
"picture": "http://placehold.it/32x32",
"age": 38,
"eyeColor": "green",
"name": {
"first": "Dunlap",
"last": "Lott"
},
"company": "FUELTON",
"email": "dunlap.lott@fuelton.biz",
"phone": "+1 (888) 407-2414",
"address": "883 Nixon Court, Wolcott, Marshall Islands, 2469",
"about": "Dolor tempor ullamco deserunt tempor sunt esse irure ut fugiat. Irure occaecat fugiat deserunt
ad. Ipsum laborum excepteur excepteur dolore qui aliqua. Ad tempor culpa commodo laborum laboris ut
amet elit est cupidatat consectetur nostrud consequat.",
"registered": "Saturday, August 5, 2017 12:57 PM",
😒

33. Duh! You should use fixtures

34. let passwordError = ErrorFixture(type: .password)
let usernameError = ErrorFixture(type: .username)
let validationError = ErrorFixture(type: .validation)
let serverError = ErrorFixture(type: .server)

35. extension AuthenticationServiceTests: AuthenticationAPI {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let json = """
{"status": "ok", "user": {"id": 1, "name": "Donny"}
""".data(using: .utf8)
callback(json, nil)
}
}

36. extension AuthenticationServiceTests: AuthenticationAPI {
func loginUser(withUsername username: String, password: String, callback: (Data?, Error?) -> Void) {
let fixture = AuthenticationFixture(type: .success)
callback(fixture.data, nil)
}
}

37. class AuthenticationServiceTests: QuickSpec {
override func spec() {
describe("The Service") {
it("Should log in") {
let service = AuthenticationService(api: self)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == "Donny"
expect(user?.id) == 1
}
}
}
}
}
We just made the hardcoded values worse…

38. Swift 4.0, to the rescue

39. Swift 4.0, to the rescue
{JSON} Decodable User

40. Swift 4.0, to the rescue
{JSON} Decodable User
Why not do this?

41. Swift 4.0, to the rescue
{JSON} Decodable User
Why not do this?
{JSON} Encodable User

42. describe("The Authentication Service") {
it("Should log in a user") {
let mockUser = User(name: "Donny", id: 1)
let userData = try! JSONEncoder().encode(mockUser)
let authenticationApi = MockAuthenticationApi(responseData: userData, error: nil)
let service = AuthenticationService(api: authenticationApi)
service.loginUser(withUsername: "Donny", password: "password") { user, error in
expect(user?.name) == mockUser.name
expect(user?.id) == mockUser.id
}
}
}
Now we’re getting somewhere!

43. struct Prize: Codable {
enum PrizeType: Int, Codable {
case regular = 0, main = 1
}
let id: Int
let type: PrizeType
let label: String
}
struct Play: Codable {
let id: Int
let acquiredPrizes: [Prize]
}
struct Game: Codable {
let id: Int
let availablePrizes: [Prize]
let name: String
let closeDate: Date
let plays: [Play]
let maxPlayCount: Int
}
struct PlayResponse {
let game: Game
let currentPlay: Play
}
But we’re not quite there

44. The final steps

45. Mockable
protocol Mockable: Codable {
associatedtype BaseType: Decodable
}
extension Mockable {
var data: Data? {
return try? JSONEncoder().encode(self)
}
var baseType: BaseType? {
guard let data = self.data
else { return nil }
return try? JSONDecoder().decode(BaseType.self, from: data)
}
}

46. Mockable
protocol Mockable: Codable {
associatedtype BaseType: Decodable
}
extension Mockable {
var data: Data? {
return try? JSONEncoder().encode(self)
}
var baseType: BaseType? {
guard let data = self.data
else { return nil }
return try? JSONDecoder().decode(BaseType.self, from: data)
}
}

47. Mockable
protocol Mockable: Codable {
associatedtype BaseType: Decodable
}
extension Mockable {
var data: Data? {
return try? JSONEncoder().encode(self)
}
var baseType: BaseType? {
guard let data = self.data
else { return nil }
return try? JSONDecoder().decode(BaseType.self, from: data)
}
}

48. Mock all the things!
class MockPrize: Mockable {
typealias BaseType = Prize
enum PrizeType: Int, Codable {
case regular = 0, main = 1
}
var id = 0
var type = PrizeType.regular
var label = "Default Label"
}
class MockPlay: Mockable {
typealias BaseType = Play
var id = 0
var acquiredPrizes = [MockPrize]()
}
class MockGame: Mockable {
typealias BaseType = Game
var id = 0
var availablePrizes = [MockPrize]()
var name = "Default game name"
var closeDate = Date()
var plays = [MockPlay]()
var maxPlayCount = 1
}
class MockPlayResponse: Mockable {
typealias BaseType = PlayResponse
var game = MockGame()
var currentPlay = MockPlay()
}

49. Mock all the things!
I know… it would be great if you could skip this!
class MockPrize: Mockable {
typealias BaseType = Prize
enum PrizeType: Int, Codable {
case regular = 0, main = 1
}
var id = 0
var type = PrizeType.regular
var label = "Default Label"
}
class MockPlay: Mockable {
typealias BaseType = Play
var id = 0
var acquiredPrizes = [MockPrize]()
}
class MockGame: Mockable {
typealias BaseType = Game
var id = 0
var availablePrizes = [MockPrize]()
var name = "Default game name"
var closeDate = Date()
var plays = [MockPlay]()
var maxPlayCount = 1
}
class MockPlayResponse: Mockable {
typealias BaseType = PlayResponse
var game = MockGame()
var currentPlay = MockPlay()
}

50. What does this give us?

51. What does this give us?
• Mutable “clones” of the models

52. What does this give us?
• Mutable “clones” of the models
• (Sensible) Default values

53. What does this give us?
• Mutable “clones” of the models
• (Sensible) Default values
• Objects that are ready to be encoded to JSON

54. What does this give us?
• Mutable “clones” of the models
• (Sensible) Default values
• Objects that are ready to be encoded to JSON
• Some spare time because we don’t need to collect mocks for each
configuration

55. What does this give us?
• Mutable “clones” of the models
• (Sensible) Default values
• Objects that are ready to be encoded to JSON
• Some spare time because we don’t need to collect mocks for each
configuration
• Typo-free comparisons

56. Now this is MotherMocking nice!
describe("When playing a game and the server returns no prizes") {
let gameData = MockGame().data
let gameApi = MockGameApi(preparedData: gameData, error: nil)
let gameService = GameService(api: gameApi)
it("The parsed model should not contain prizes") {
gameService.play { game, error in
expect(game?.plays.first?.acquiredPrizes.count) == 0
}
}
}

57. Now this is MotherMocking nice!
describe("When playing a game and the server returns a main prize") {
let game = MockGame()
let play = MockPlay()
let prize = MockPrize()
prize.type = .main
play.acquiredPrizes = [prize]
game.plays = [play]
let gameApi = MockGameApi(preparedData: game.data, error: nil)
let gameService = GameService(api: gameApi)
it("The parsed model should contain a single main prize") {
gameService.play { game, error in
expect(game?.plays.first?.acquiredPrizes.count) == 1
expect(game?.plays.first?.acquiredPrizes.first?.type) == .main
}
}
}

58. Easier configuration of mocks
encourages testing more cases

59. What is not easier with this approach?

60. What is not easier with this approach?
• It’s hard to test what your code does if you get malformed json

61. What is not easier with this approach?
• It’s hard to test what your code does if you get malformed json
• You can’t purposefully omit certain properties (unless you make a special
mock class for that case)

62. What is not easier with this approach?
• It’s hard to test what your code does if you get malformed json
• You can’t purposefully omit certain properties (unless you make a special
mock class for that case)
• You still need a single source of truth for what data goes into a model. You
could coordinate some sort of setup with the back-end team so you can
fetch a blueprint for each model

63. Some final notes

64. Some final notes
• It’s easier to mock responses if your api services return Data instead of
models

65. Some final notes
• It’s easier to mock responses if your api services return Data instead of
models
• Make smaller services so you can easily create focussed mocks for them

66. Some final notes
• It’s easier to mock responses if your api services return Data instead of
models
• Make smaller services so you can easily create focussed mocks for them
• Your tests shouldn’t rely on a network connection

67. Some final notes
• It’s easier to mock responses if your api services return Data instead of
models
• Make smaller services so you can easily create focussed mocks for them
• Your tests shouldn’t rely on a network connection
• This (obviously) is not a silver bullet

68. Some final notes
• It’s easier to mock responses if your api services return Data instead of
models
• Make smaller services so you can easily create focussed mocks for them
• Your tests shouldn’t rely on a network connection
• This (obviously) is not a silver bullet
• Large or complex configurations can still be fed to Mockable objects since
they conform to Codable

69. #