Best practices for unit testing RxJava

Simon Perčič, senior Android developer

Tuesday, November 8th, 2016 @ 18:00

RxJava?

● Useful for combining, transforming, manipulating streams of data

● How to unit test?

What to unit test?

● Observables - composition of operators

● Code that uses Rx (e.g. presenters)

Let’s set an example

What will we test?

What will we test?

DataManager methods:

Tip #1 (testability)

Tip #1Separate data providers

Test skeleton 1/3

mocked

subject of testing

Test skeleton 2/3

Test skeleton 3/3

Test examples*

* not best practices

Wrong test #1

Works. → But only if getPlanets() is run on the immediate thread

Wrong test #1

Works. → But only if getPlanets() is run on the immediate thread

Not immediate thread

Runs on another thread!

Wrong test #1 - on another thread

Fails. → getPlanets() switches thread, Assert happens “too soon”

Wrong test #2 - blocking

Works. → it waits for the getPlanets() single to complete.

Wrong test #2 - countdown

Blocks here

Tip #2 (threading)

Tip #2

Single / Observable transformer

Network thread

Tip #2 - in manager

Compose with scheduler transformer

Tip #2 - in test

No op transformation.

Tip #3 (the big one)*

* best practices

Built-in classes

● TestSubscriber

● TestScheduler

● TestSubject

Tip #3 [1/3] - TestSubscriber

● Subscriber with additional test methods

● Part of RxJava

TestSubscriber example

● Blocking○ awaitTerminalEvent()

TestSubscriber methods

Will block

● Assertions○ Completion

■ assertCompleted() / assertNotCompleted()■ assertTerminalEvent() / assertNoTerminalEvent()

TestSubscriber methods

● Assertions○ Errors

■ assertNoErrors()■ assertError(Class / Throwable)

TestSubscriber methods

● Assertions○ Values

■ assertNoValues()■ assertValueCount(int)■ assertValue(T) / assertValues(T…)

TestSubscriber methods

● Get values○ Values

■ List<T> getOnNextEvents()○ Errors

■ List<Throwable> getOnErrorEvents()

TestSubscriber methods

Tip #3 [2/3] - TestScheduler

● Time “manipulation”○ Advance time

■ advanceTimeBy(long, TimeUnit)■ advanceTimeTo (long, TimeUnit)

○ Force trigger■ triggerActions()

TestScheduler methods

Tip #3 [3/3] - TestSubject

● Enables us to queue events with a delay○ onNext(T, delayMs)○ onCompleted(delayMs)○ onError(Throwable, delayMs)

TestSubject - setup

TestSubject - test

● Use RxJava

● Make your code unit-testable

● Be aware of threading

● Use built-in testing utils

Recap

Questions?

@simonpercic @simonpercicsimonpercic