Best practices for unit testing RxJava

You've undoubtedly heard of RxJava. You probably started using it and instantly fell in love. You decided you're not going back, ever. Your code is now beautifully Rx-ified. Now, how can you test that it does what it's supposed to? In this talk, we'll look at the different options you have when writing unit tests for your Rx-powered code.

Transcript

1. Best practices for unit testing RxJava Simon Perčič, senior Android developer Tuesday, November 8th, 2016 @ 18:00
2. RxJava? • Useful for combining, transforming, manipulating streams of data • How to unit test?
3. What to unit test? • Observables - composition of operators • Code that uses Rx (e.g. presenters)
4. Let’s set an example
5. What will we test?
6. What will we test? DataManager methods:
7. Tip #1 (testability)
8. Tip #1 Separate data providers
9. Test skeleton 1/3 mocked subject of testing
10. Test skeleton 2/3
11. Test skeleton 3/3
12. Test examples* * not best practices
13. Wrong test #1 Works. → But only if getPlanets() is run on the immediate thread
14. Wrong test #1 Works. → But only if getPlanets() is run on the immediate thread
15. Not immediate thread Runs on another thread!
16. Wrong test #1 - on another thread Fails. → getPlanets() switches thread, Assert happens “too soon”
17. Wrong test #2 - blocking Works. → it waits for the getPlanets() single to complete.
18. Wrong test #2 - countdown Blocks here
19. Tip #2 (threading)
20. Tip #2 Single / Observable transformer Network thread
21. Tip #2 - in manager Compose with scheduler transformer
22. Tip #2 - in test No op transformation.
23. Tip #3 (the big one)* * best practices
24. Built-in classes • TestSubscriber • TestScheduler • TestSubject
25. Tip #3 [1/3] - TestSubscriber • Subscriber with additional test methods • Part of RxJava
26. TestSubscriber example
27. • Blocking ◦ awaitTerminalEvent() TestSubscriber methods Will block
28. • Assertions ◦ Completion ▪ assertCompleted() / assertNotCompleted() ▪ assertTerminalEvent() / assertNoTerminalEvent() TestSubscriber methods
29. • Assertions ◦ Errors ▪ assertNoErrors() ▪ assertError(Class / Throwable) TestSubscriber methods
30. • Assertions ◦ Values ▪ assertNoValues() ▪ assertValueCount(int) ▪ assertValue(T) / assertValues(T…) TestSubscriber methods
31. • Get values ◦ Values ▪ List<T> getOnNextEvents() ◦ Errors ▪ List<Throwable> getOnErrorEvents() TestSubscriber methods
32. Tip #3 [2/3] - TestScheduler
33. • Time “manipulation” ◦ Advance time ▪ advanceTimeBy(long, TimeUnit) ▪ advanceTimeTo (long, TimeUnit) ◦ Force trigger ▪ triggerActions() TestScheduler methods
34. Tip #3 [3/3] - TestSubject • Enables us to queue events with a delay ◦ onNext(T, delayMs) ◦ onCompleted(delayMs) ◦ onError(Throwable, delayMs)
35. TestSubject - setup
36. TestSubject - test
37. • Use RxJava • Make your code unit-testable • Be aware of threading • Use built-in testing utils Recap
38. Questions? @simonpercic @simonpercic simonpercic