1. The document introduces Swift Localhost, a tool for writing localhost UI tests in Swift. It allows setting up a mock localhost server to handle API requests from the app under test. 2. Common problems with traditional end-to-end tests like brittle tests and slow execution are discussed. Localhost UI tests address these by mocking API responses at a faster, isolated integration level. 3. The key aspects of setting up and asserting localhost requests are explained, including routing requests to the localhost server, configuring mock responses, and validating the expected request paths and cURL commands.

1. Introducing API Contract
and Localhost UI Tests
Kenneth Poon
https://medium.com/@kennethpoon
App Development Integration Tests

2. https://medium.com/@kennethpoon
https://github.com/depoon
Kenneth Poon
https://sg.linkedin.com/in/kenneth-poon-84217019
de_poon@hotmail.com
Principal Software Engineer @ SP Digital
Agile Development in iOS Development Space
Tech talk contributor in iOS Dev Scout Meetup group in Singapore
About me

3. Testing Testing
Past talks
https://engineers.sg/presenter/kenneth-poon--533
Testing
iOS Dev Scout
Meetup
iOS Conf SG 2019
Agile Singapore
Testing
Mobile Conf TH

4. Past talks
https://engineers.sg/presenter/kenneth-poon--533
iOS Dev Scout
Meetup
HackingHacking
Development

5. Agenda
Contract Tests (Ruby) - Cucumber API
Background and motivation for this sharing this talk
Localhost UI Test (iOS) - Swift Localhost

6. Background and Motivation
J2EE -> iOS Development
Not much iOS Test + CI Practices out there (2010)
Sinatra (Ruby)Calabash (Ruby) Cucumber (Ruby)
SwiftLocalhost (Swift)Cucumberish (Swift)

7. Life of a Mobile Developer
Mobile Developer Backend EngineerQA
I’m a mobile developer.
In terms of testing, I
write Unit tests to
ensure that my
modules are working
as expected.
I will also ensure that I
achieve high code
coverage for my native
app codes
I’m a QA engineer. I take
ownership of mobile
E2E tests.
When the mobile app
build is ready , I will
verify it in our test/QA
environment
I’m a backend engineer.
I write tests that cover
the behaviour of the
services I build.

8. Life of a Mobile Developer
Mobile Developer Backend Engineer
API Contract
Feature
1
Not Readyv1
v1

9. Life of a Mobile Developer
Mobile Developer Backend EngineerAPI Contract
Feature
1
v1
v1

10. Life of a Mobile Developer
Mobile Developer Backend EngineerAPI Contract
Feature
1
v1
v1
V2
v1
App Breaks - API Contract
• Contract definition has changed
• Backend Engineer may not be
aware of what services app is
consuming
• QA may only find out after running
test suite
APPLICATION
BREAKS
QA: WHAT’S HAPPENING!!

11. Life of a Mobile Developer
Mobile Developer
Feature
1

12. Life of a Mobile Developer
Mobile Developer
Feature
1
Database 3rd Party Services
App Breaks - Dependencies
• Services down
• Test Data Fixtures are not
synced up
• Engineers may only discover
broken dependencies by
running E2E tests
APPLICATION
BREAKS
QA: My E2E Tests
failed again!
What is happening
this time?

13. Life of a Mobile Developer
Mobile Developer QA

14. Life of a Mobile Developer
Mobile Developer QA
Dev, the app is breaking
very often in Test/
Staging environment
Sorry about it, QA.
My native code is
fine. It seems like
the backend
services are down
at the moment
Grrr.. it took me an hour
of tests execution just
to discover that that.
This is driving me crazy.
Other times, the backend engineer
unknowingly changed the API schema I understand but I will always find
you first whenever I discover any of
these issues.
Hmmm… let me come up with a
solution for this

15. About End-to-End Tests
QA
As QA, we own and take responsibility in the development
and maintenance of the mobile E2E tests
But E2E tests are very brittle
Mobile Apps typically have multiple dependencies
Difficult to write tests that are dependent on shared
resources
E2E Tests are generally slow and expensive
Even if we can write E2E tests, we may not be
able to achieve comprehensive UI Automation
test coverage

16. Test Pyramid
Unit Tests
E2E Tests
Integration
Tests
XCUITest / Appium
XCTest / JUnit
API Contract Tests
Mock Response Tests

17. Integration Tests
Api Contract Tests
Mock
Mock Response Tests
Mock
Localhost
Localhost XCUITest - iOS SwiftLocalhost

18. Setup
Swift Localhost
Tests
Unit Tests
E2E Tests
Integration
Tests
Mock Response Tests

19. L
A
I
M
[Localhost] Setup in-memory localhost server
[API] Redirect API calls to localhost server
[Info.plist] Patch Info.plist
[Mock] Setup mock responses
Setup Localhost

20. Setup Localhost - [Localhost]
Localhost
Server
Use a unique port number
Setup an in-memory server in the test runner
Setup and tear down localhost server when
executing each test

21. import XCTest
class MovieListTest: XCTestCase {
}
import SwiftLocalhost
var localhostServer: LocalhostServer!
override func setUp() {
}
self.localhostServer =
LocalhostServer(portNumber: 9001)
self.localhostServer.startListening()
override func tearDown() {
}
Setup Localhost - [Localhost]
self.localhostServer.stopListening()
self.localhostServer =
LocalhostServer.initializeUsingRandomPortNumber()

22. Setup Localhost - [API]
Localhost
Server
Actual
Server
Update URL Domain to localhost
(with port number)

23. private let baseUrl: String = "http://localhost:9001/3/movie"
Setup Localhost - [API]
class NetworkOperations {
}
private let baseUrl: String = "https://api.themoviedb.org/3/movie"//private let baseUrl: String = "https://api.themoviedb.org/3/movie"

24. Setup Localhost - [Info.plist]
Localhost
Server Update Info.plist
iOS >=10
iOS 9

25. path["/login"] = {
“status" = "login successful"
}
path["/movies"] = [
{
"title": "Batman",
"subtitle": "XXX"
},
{
“title": "Matrix",
"subtitle: "YYY"
},
]
Setup Mock
Responses
Setup Localhost - [Mock]
Localhost
Server

26. func testMoviePopularList() {
}
XCUIApplication().launch()
//Add XCUITest Codes
Setup Localhost - [Mock]
self.localhostServer.route(method: .GET,
path: "/3/movie/popular",
responseJsonFileName: "home_popular")

27.
Asserting
Localhost
Requests
Unit Tests
E2E Tests
Integration
Tests
Mock Response Tests

28. List
Asserting Localhost Requests
Use case
1. Listing View
Item List Request
Localhost Requests

29. Asserting Localhost Requests
Use case
1. Listing View
2. Detail View Item List Request
Localhost Requests
Detail
Item Detail Request

30. Asserting Localhost Requests
Use case
1. Listing View
2. Detail View Item List Request
Localhost Requests
Detail
Item Detail Request
3. Bookmark Item
Bookmark Item Request
Expected Requests Order

31. Asserting Localhost Requests
public class LocalhostServer {
public var recordedRequests: [URLRequest]
}
LocalhostServer records all received URLRequest(s)

32. Asserting Localhost Requests
//#### By URL Paths---------
let expectedRequestPaths: [String] = [
"/3/movie/popular",
"/identitytoolkit/v3/relyingparty/verifyPassword",
"/identitytoolkit/v3/relyingparty/getAccountInfo"
]
let actualRequestPaths = self.localhostServer.recordedRequests.map {
return $0.url!.path
}
XCTAssertEqual(expectedRequestPaths, actualRequestPaths)

33.
let expectedCURLs: [String] = [
"curl -X GET ’http://localhost:9001/3/movie/popular?api_key=71b'",
"curl -X POST ’http://localhost:9001/relyingparty/verifyPassword?
key=AIzaSy' -d '{n "email" : "apple@gmail.com",n "password" :
"password"}'",
"curl -X POST ’http://localhost:9001/relyingparty/getAccountInfo?
key=AIzaSy' -d '{n "idToken" : "eyJhbj"n}'"
]
let expectedCURLs: [String] = [
"curl -X GET ’http://localhost:9001/3/movie/popular?api_key=71b'",
"curl -X POST ’http://localhost:9001/relyingparty/verifyPassword?
key=AIzaSy' -d '{n "email" : "apple@gmail.com",n "password" :
"password"}'",
"curl -X POST ’http://localhost:9001/relyingparty/getAccountInfo?
key=AIzaSy' -d '{n "idToken" : "eyJhbj"n}'"
]
let actualCURLs = self.localhostServer.recordedRequests.map {
return $0.cURL(withHeaders: false)
}
Asserting Localhost Requests
//#### By describing cURL commands ---------
XCTAssertEqual(expectedCURLs, actualCURLs)
let expectedCURLs: [String] = [
"curl -X GET ’http://localhost:9001/3/movie/popular?api_key=71b'",
"curl -X POST ’http://localhost:9001/relyingparty/verifyPassword?
key=AIzaSy' -d '{n "email" : "apple@gmail.com",n "password" :
"password"}'",
"curl -X POST ’http://localhost:9001/relyingparty/getAccountInfo?
key=AIzaSy' -d '{n "idToken" : "eyJhbj"n}'"
]

34. https://github.com/mkamhawi/ios-movies-app [orginal]
Special Thanks to
Mohamed El-Kamhawi
https://github.com/depoon/ios-movies-app [forked]
Swift Localhost
Demo
Unit Tests
E2E Tests
Integration
Tests
Mock Response Tests

35. FAQ on Localhost UITests
Why can’t we add stub responses in the code?
Localhost
Server
Mock
HTTP
TCP
HTTP
TCP
Mock
Response

36. FAQ on Localhost UITests
Swift Localhost Vapor (Swift)
WireMock (Java)
Typicode (JS)
Sinatra (Ruby)
What are the advantages of using Swift Localhost over other localhost
web server solutions?

37. FAQ
Swift Localhost
Vapor (Swift)
WireMock (Java)
Typicode (JS)
Sinatra (Ruby)
What are the advantages of using Swift Localhost over other localhost
web server solutions?

38. FAQ on Localhost UITests
Swift Localhost
Vapor (Swift)
WireMock (Java)
Typicode (JS)
Sinatra (Ruby)
What are the advantages of using Swift Localhost over other localhost
web server solutions?
Advantages
✓ Easy Installation and Setup via Cocoapods
✓ Use Swift to setup mock server
✓ In line mock responses in the same test scope
✓ Use same runtime XCode debugger
✓ Ctrl + U

39. FAQ
How does the Localhost UITest technique fit in my development
process?
List
2. Fetch list of items using server/list api
1. Navigate to List view
3. Tap on 1st Item. App navigates to Detail view
4. Fetch item detail using server/detail api
5. Bookmark item
6. Bookmark item detail using
server/bookmark api
Bookmarking Use Case
DetailDetail
server/list
server/detail
server/bookmark
7. Assert Bookmark Icon is correctly reflected

40. FAQ
How does the Localhost XCUITest technique fit in my development
process?
Detail
server/list
server/detail
server/bookmark
Localhost Mock Responses
Test Case
1. Navigate to List view
2. Tap on 1st Item. App navigates to Detail view
3. Bookmark item
4. Assert Bookmark Icon is correctly reflected
Never Ever Fails
✓ Early Development
✓ Use Case Wont Fail

41. API Contract
Tests
Unit Tests
E2E Tests
Integration
Tests
API Contract Tests

42. API Contract Tests
Mobile Developer QA
Dev, I know it’s great
that you have Mock
Response Tests that
never fails.
But the APIs do change
and they might break
the app.
Yes, QA. You are
absolutely right
API Contract
v1
But our app
releases are
bounded by the
pre-agreed
APIContracts
We can write a script to ensure the
APIs are working as agreed upon
We can use this script to discover
which services are affecting the app.

43. API Contract Tests
API Contract
v1

44. API Contract Tests
API Contract
v1 /v1/login -> schema1_v1
/v1/shoppingList -> schema2_v1
/v1/productDetails -> schema3_v1
/v1/productDetails -> schema4_v1
API Contract Script
v1 v1.1 V2
/v1/productDetails -> schema3_v2
Mobile Developer
Gotcha! Latest
API deployment
broke our app

45. API Contract Tests
Backend Engineer
Hey Mobile Dev,
Why are you writing
tests against my
API? Shouldn’t I be
the one responsible
for that?
Mobile Developer
Our app will
perform correctly
only when
dependent services
are working as
expected.
Our API Contract tests will give you quick feedback
whenever deployed services break the contracts
Mobile developers will be responsible to maintain
tests that describe the services the app consume.

46. API Contract Tests
Backend Engineer
That sounds
awesome to me.
You know what? I
think we should
automatically
trigger the API
Contract tests
every time we
deploy any changes
Mobile Developer
Nice! This encourages backend developers to
deploy changes without worrying whether it
will affect the mobile app clients.
… BECAUSE WE WILL CATCH ANY BREAKING CHANGES

47. API Contract Tests
Mobile Developer QA
Dev, I feel annoyed that
after running my tests, I
discover my test
fixtures are not ready
(or incorrect).
eg. Login credentials,
Product Details on
Staging environment
are incorrect
Your test cases
actually describe
the request/
response exchange
that will be
expected.
We can write API Contract tests that chain the order
of API requests that simulates a use case on the app
You can simply run the API Contract tests before any
automated/manual execution of tests. This will give
you a headsup whether your tests will fail
Since API Contract tests are generally fast, you will
get your feedback in no time.
Wow, this sounds
awesome. I am
eager to have a go
at it

48. Introducing
Cucumber API
Unit Tests
E2E Tests
Integration
Tests
API Contract Tests

49. What is your take on API Contract Tests (ACT)
Mobile Developer Backend EngineerQA
ACT checks whether
our app dependencies
are working as
expected.
The contract definition
aids us in designing
our localhost tests
ACT is a cheap and fast
way for QA to ensure
that all dependencies,
including data fixtures
are ready before we
start testing.
The fast feedback saves
us time especially when
we can get feedback
within seconds
With ACT, I have more
confidence to refactor
my code base.
We are now
encouraged to run ACT
tied to released app
versions and check if
older versions will be
broken by new API code
deployments

50. Closing
Consider having both Mock Response and API Contract Tests
Integration tests are meant to compliment but not replace E2E
API Contract Tests is the low hanging fruit
Confidently run localhost tests to verify that native app codes is
working under normal, valid conditions
It may be difficult (but not impossible) to mock services used by 3rd party
services.
Do visit your existing tools and see how you can bring integration tests
into your development

51. https://medium.com/better-programming/how-to-import-
swift-urlrequests-into-postman-ef6c65c20834
https://github.com/depoon/SwiftLocalhost
https://github.com/hidroh/cucumber-api
https://github.com/depoon/ios-movies-app
Demo App
Import Swift URLRequests into Postman
Setting up Swift localhost for testing
Cucumber API
References

52. References
https://bit.ly/2ZbDcA3
https://medium.com/@kennethpoon

53. Questions