Deep Dive Into Coroutine Testing @mambo_bryan 01

02 Design Centric Engineer Brian Odhiambo Dishwasher @ Baobab Circle Co-organizer @ KotlinKenya Maintaining @ KotlinBits Crazy about that UI/UX & Kotlin

Ensuring It Works 03 testing! assertions! failures! Suspending Functions Testing functions that immediately return a value Non Suspending Functions Testing functions that launch other coroutines

What are coroutines? What are coroutine builders? A Small Recap Why use coroutines? What is a coroutine context, why do we need it? What are jobs, and their state? What are dispatchers and how do they help? And So much more... Just like DSTV

Testing The theory of testing

improve code quality detect vulnerabilities detect edge cases early being kind to the next developer so on & so forth Evaluating and verifying the accuracy of your code What is testing? Why should we test?

improve code quality detect vulnerabilities detect edge cases early being kind to the next developer so on & so forth Evaluating and verifying the accuracy of your code What is testing? Why should we test? action performed WHEN expected outcome of the action SHOULD Thing under test GIVEN

Example fun add(a : Int, b : Int) = a.plus(b) fun main() { // given & when val actual = add(1, 2) val expected = 3 // should if(expected != actual) println("Test Failed !") else println("Test Passed...") } 06

runBlocking { ... } runBlockingTest { ... } Evolution Of kotlinx.coroutines.test runTest { ... }

Suspending Testing suspended functions

suspend fun fetchAuthors() { delay(1_500L) return listOf("a", "b", "c") } @Test fun fetchAuthorsTest(){ val list = fetchAuthors() assertContains(list, "a") } 06

suspend fun fetchAuthors() { delay(1_500L) return listOf("a", "b", "c") } @Test fun fetchAuthorsTest(){ val list = fetchAuthors() assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest suspend fun fetchAuthors() { delay(1_500L) return listOf("a", "b", "c") } @Test fun fetchAuthorsTest() = runTest { val list = fetchAuthors() assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest suspend fun fetchAuthors() = withContext(Dispatchers.IO) { delay(1_500L) return listOf("a", "b", "c") } @Test fun fetchAuthorsTest() = runTest { val list = fetchAuthors() assertContains(list,"a") } 06

New Coroutines Those fire & forget coroutines

runBlocking { ... } runBlockingTest { ... } runTest { ... } TestCoroutineScheduler TestDispatcher Evolution Of kotlinx.coroutines.test runTest { ... } TestScope

import kotlinx.coroutines.text.runTest suspend fun fetchAuthors(dispatcher: CoroutineContext) = withContext(dispatcher) { delay(1_500L) return listOf("a", "b", "c") } @Test fun fetchAuthorsTest() = runTest { val list = fetchAuthors(testDispatcher) assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest ... fun addAuthors() { launch { database.add("a") } launch { database.add("b") } } fun fetchAuthors(){ return authors } ... @Test fun fetchAuthorsTest() = runTest { val repo = AuthorRepository() repo.addAuthors() val list = fetchAuthors() assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest ... fun addAuthors() { launch { database.add("a") } launch { database.add("b") } } fun fetchAuthors(){ return authors } ... @Test fun fetchAuthorsTest() = runTest { val repo = AuthorRepository() repo.addAuthors() val list = fetchAuthors() assertContains(list,"a") } 06

starts job immediately use selectively UnconfinedTestDispatcher default dispatcher queues work StandardTestDispatcher TestDispatchers

import kotlinx.coroutines.text.runTest ... fun addAuthors() { launch { database.add("a") } launch { database.add("b") } } fun fetchAuthors(){ return authors } ... @Test fun fetchAuthorsTest() = runTest { val repo = AuthorRepository() repo.addAuthors() advanceUntilIdle() val list = fetchAuthors() assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest ... fun addAuthors() { launch { database.add("a") } launch { database.add("b") } } fun fetchAuthors(){ return authors } ... @Test fun fetchAuthorsTest() = runTest(UnconfinedTestDispatcher()) { val repo = AuthorRepository() repo.addAuthors() // advanceUntilIdle() val list = fetchAuthors() assertContains(list,"a") } 06

import kotlinx.coroutines.text.runTest class AuthRepository(scope: CoroutineContext){ fun addAuthors() { scope.launch { database.add("a") } scope.launch { database.add("b") } } fun fetchAuthors(){ return authors } ... @Test fun fetchAuthorsTest() = runTest() { val repo = AuthorRepository(testDispatcher) repo.addAuthors() val list = fetchAuthors() assertContains(list,"a") } 06

One Last Thing For the community

KotlinBits 😎 A fun and easy way to learn Kotlin in small bits and pieces. React, Comment & Share https://kotlinbits.vercel.app

Thank you So much DroidPwani. You guys have been awesome & fantastic

16 mambo_bryan MamboBryan Have a nice Kotlin KotlinBits kotlinbits.vercel.app