In this talk we'll consider principles of designing easy-to-test interfaces that help to build quality tests including discussions of different dependency management techniques both in Swift and Objective-C. For product companies like Badoo, high quality products are important. New code is being produced and shipped fast with new features continuously delivered to users. One way of verifying a feature's quality is covering related code with unit tests. We'll talk about principles that help developers design easy-to-test interfaces and improve the tests quality both in Swift and Objective-C with real examples from Badoo app.

1. Design for Testability
Anton Schukin, iOS Developer
twitter: @antonpalich

2. My History
2013 - 2015
2015 - Now

3. My History
2013 - 2015
2015 - Now

4. 320M+ registered users
190 countries
46 languages
50M+ downloads (iOS)

5. Overview
1. Unit Testing in Badoo
2. F.I.R.S.T
3. Unit Testing in practice

6. 11 developers
iOS Team

7. 11 developers, weekly releases:
~ 300 commits
~ 1 000 files changed
iOS Team

8. 11 developers, weekly releases:
~ 300 commits
~ 1 000 files changed
~ 50 000 insertions
~ 63 000 deletions (Legacy code removals)
iOS Team

9. New Features
Changes

10. New Features
Bug fixing
Changes

11. New Features
Bug fixing
Technical debts
Changes

12. Code Coverage
20
25
30
35
40
Sep Oct Nov Dec Jan Feb Mar Apr May June July Aug Sep
from 23.47% to 36.47% (70675 / 193726 lines)

13. Find problem earlier
Unit Testing - WHY?

14. Find problem earlier
Regression tests for changes
Unit Testing - WHY?

15. Find problem earlier
Regression tests for changes
Live documentation
Unit Testing - WHY?

16. Unit Testing - WHAT?

17. Unit Testing - WHAT?
State
Interaction with dependencies

18. Unit Testing - WHAT?
State
Interaction with dependencies
MVP MVC
MVVM VIPER

19. F.I.R.S.T*
• Fast
• Independent
• Repeatable
• Self-validating
• Timely
*Robert C. Martin «Clean Code»

20. Fast
1s 100ms 10ms
100 tests 1m 40s 10s 1s
1000 tests 16m 40s 1m 40s 10s
4000 tests 1h 6m 40s 6m 40s 40s

21. Fast
1s 100ms 10ms
100 tests 1m 40s 10s 1s
1000 tests 16m 40s 1m 40s 10s
4000 tests 1h 6m 40s 6m 40s 40s

22. Fast
3877 tests in 79.66s (~49ms per test)*
* MacBook Pro Retina (Early 2013), 2.7 GHz i7, 16GB 1600 MHz

23. Independent
T1
Sandbox
T2 T3 T4
+[NSUserDefaults standardUserDefaults]

24. Independent
T1
Sandbox
Mock
T2
Sandbox
Mock
T3
Sandbox
Mock
T4
Sandbox
Mock

25. Repeatable
T1
Dev 1
Result
T1
Dev 2
Result
T1
CI 1
Result
T1
CI 2
Result== == ==

26. Self-validating
PASSED OR FAILED

27. Timely

28. Timely
Dev Polishing
Test after code
for code coverage

29. Timely
Dev Polishing
Dev Polishing
Test after code
for code coverage
Test after code
for value

30. Timely
Dev
Dev Polishing
Dev Polishing
Test after code
for code coverage
Test after code
for value
TDD

31. New Feature
Download user photos

32. New Feature
Download user photos
Store compressed and original photos

33. New Feature
Download user photos
Store compressed and original photos
Do it no more than every four hours

34. New Feature
Download user photos
Store compressed and original photos
Do it no more than every four hours
Do it when your app becomes active

35. Code Example
https://github.com/AntonPalich/NSSpain16Example

36. Conclusion
Think about interfaces first

37. Conclusion
Think about interfaces first
Unit tests is your friend

38. Conclusion
Think about interfaces first
Unit tests is your friend
TDD saves developer time

39. Conclusion
Think about interfaces first
Unit tests is your friend
TDD saves developer time
TAD (Test after development) also fine

40. Thank you!
We’re hiring
twitter: @BadooTech
github.com/Badoo