Android Worldwide TDD in Android

Presented at Android Worldwide conference 2022.
Most developers (who writes test cases, but doesn't yet follow TDD) are interested in or willing to follow TDD, the only factor stopping them from following TDD is confusion.
In this session, I'll try to remove that confusion, so that developers can follow TDD without hesitation.
I'll be talking about following TDD, what should be the process, and how exactly should you approach TDD.

Transcript

1. TDD in Android
   Rivu Chakraborty
   https://www.rivu.dev/
   AndroidWorldwide
   

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2. Rivu Chakraborty
   @rivuchakraborty
   https://www.rivu.dev
   Android @
   

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3. Types of Tests
   https://www.rivu.dev/
   https://www.rivu.dev/
   

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4. Test Pyramid
   Unit Tests
   Integration Tests
   E2E Tests
   

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5. Unit Tests
   @Test
   fun `test getUsers`() = runBlocking {
   val expected = getDummyUsers()
   val result = testUserRepository.getUsers()
   assertEquals(expected, result)
   }
   

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6. Integration Tests
   @Test
   fun `test getUsers`() = runBlocking {
   val expected = localDS.getUsers() //Actual Local DS
   val result = testUserRepository.getUsers().first()
   assertEquals(expected, result)
   }
   

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7. What is TDD????
   https://www.rivu.dev/
   https://www.rivu.dev/
   

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8. Test Driven Development
   ● Write Tests, let them fail and then write Implementation
   https://www.rivu.dev/
   

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9. Test Driven Development
   ● Write Tests, let them fail and then write Implementation
   ● We want Tests to fail first
   https://www.rivu.dev/
   

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10. Test Driven Development
    ● Write Tests, let them fail and then write Implementation
    ● We want Tests to fail first
    ● Steps
    ○ Write the Interface
    https://www.rivu.dev/
    

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11. Test Driven Development
    ● Write Tests, let them fail and then write Implementation
    ● We want Tests to fail first
    ● Steps
    ○ Write the Interface
    ○ Design the Flow
    https://www.rivu.dev/
    

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12. Test Driven Development
    ● Write Tests, let them fail and then write Implementation
    ● We want Tests to fail first
    ● Steps
    ○ Write the Interface
    ○ Design the Flow
    ○ Implement the methods with TODO (We still want them to compile 😉)
    https://www.rivu.dev/
    

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13. Test Driven Development
    ● Write Tests, let them fail and then write Implementation
    ● We want Tests to fail first
    ● Steps
    ○ Write the Interface
    ○ Design the Flow
    ○ Implement the methods with TODO (We still want them to compile 😉)
    ○ Write the Tests and let them fail
    https://www.rivu.dev/
    

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14. Test Driven Development
    ● Write Tests, let them fail and then write Implementation
    ● We want Tests to fail first
    ● Steps
    ○ Write the Interface
    ○ Design the Flow
    ○ Implement the methods with TODO (We still want them to compile 😉)
    ○ Write the Implementation, make sure the tests pass now
    https://www.rivu.dev/
    

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15. Let’s do it
    https://www.rivu.dev/
    https://www.rivu.dev/
    

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16. Write the Interface
    interface ArticlesRepository {
    fun getArticles(): Flowable>
    fun fetchAndSyncArticles(): Single>
    }
    https://www.rivu.dev/
    

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17. Design the Flow
    https://www.rivu.dev/
    ● getArticles() should return from Local first and then after syncing should
    return from Remote
    ○ Should ignore empty data and errors from local and emit from Remote
    ○ If Remote also fails, should show error
    

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18. Design the Flow
    https://www.rivu.dev/
    ● getArticles() should return from Local first and then after syncing should
    return from Remote
    ○ Should ignore empty data and errors from local and emit from Remote
    ○ If Remote also fails, should show error
    ● fetchAndSyncArticles() should fetch from Remote, save it in local and emit
    the data returned from Remote
    

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19. Break down of
    Steps
    ● Create Interface
    https://www.rivu.dev/
    interface ArticlesRepository {
    fun getArticles(): Flowable>
    fun fetchAndSyncArticles(): Single>
    }
    

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20. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementations
    https://www.rivu.dev/
    class ArticlesRepositoryImpl(
    private val localDataStore: ArticlesDataStore,
    private val remoteDataStore: ArticlesDataStore
    ) : ArticlesRepository {
    override fun getArticles(): Flowable> {
    TODO("Not yet Implemented")
    }
    override fun fetchAndSyncArticles(): Single> {
    TODO("Not yet Implemented")
    }
    }
    

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21. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementations
    https://www.rivu.dev/
    class ArticlesRepositoryImpl(
    private val localDataStore: ArticlesDataStore,
    private val remoteDataStore: ArticlesDataStore
    ) : ArticlesRepository {
    override fun getArticles(): Flowable> {
    TODO("Not yet Implemented")
    }
    override fun fetchAndSyncArticles(): Single> {
    TODO("Not yet Implemented")
    }
    }
    

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22. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    Fakes
    class FakeSuccessDataStore(val data: List): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(data)
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeSaveDataStore: ArticlesDataStore {
    val articles: MutableList = mutableListOf()
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.fromCallable {
    articles.clear()
    articles.addAll(articleList)
    }
    }
    class FakeEmptyDataStore: ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeErrorDataStore(val error: Exception): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    

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23. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    Fakes
    class FakeSuccessDataStore(val data: List): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(data)
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeSaveDataStore: ArticlesDataStore {
    val articles: MutableList = mutableListOf()
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.fromCallable {
    articles.clear()
    articles.addAll(articleList)
    }
    }
    class FakeEmptyDataStore: ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeErrorDataStore(val error: Exception): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    

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24. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    Fakes
    class FakeSuccessDataStore(val data: List): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(data)
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeSaveDataStore: ArticlesDataStore {
    val articles: MutableList = mutableListOf()
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.fromCallable {
    articles.clear()
    articles.addAll(articleList)
    }
    }
    class FakeEmptyDataStore: ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeErrorDataStore(val error: Exception): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    

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25. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    Fakes
    class FakeSaveDataStore: ArticlesDataStore {
    val articles: MutableList = mutableListOf()
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.fromCallable {
    articles.clear()
    articles.addAll(articleList)
    }
    }
    class FakeEmptyDataStore: ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.just(emptyList())
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.complete()
    }
    }
    class FakeErrorDataStore(val error: Exception): ArticlesDataStore {
    override fun getArticles(): Single> = Single.defer {
    Single.error(error)
    }
    override fun saveArticles(articleList: List): Completable =
    Completable.defer {
    Completable.error(error)
    }
    }
    

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26. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    fetchAndSyncArticles
    @Test
    fun `fetchAndSyncArticles should emit remote data`() {
    /*When remote returns data, save it to DB
    *and emit the same */
    //Setup
    val dummyData = TestDataFactory.dummyArticlesList
    val localDS = FakeSaveDataStore()
    val remoteDS = FakeSuccessDataStore(dummyData)
    val articlesRepo = ArticlesRepositoryImpl(localDS,
    remoteDS)
    //When
    val testObserver =
    articlesRepo.fetchAndSyncArticles().test()
    //Then
    testObserver.assertValue(dummyData)//emitted remote
    data
    assertEquals(dummyData, localDS.articles)//saved it
    to localDS
    }
    

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27. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    getArticles
    @Test
    fun `getArticles should emit EmptyResultSetException`() {
    /*When both DS emits empty data
    * It should emit EmptyResultSetException */
    //Setup
    val localDS = FakeEmptyDataStore()
    val remoteDS = FakeEmptyDataStore()
    val articlesRepo = ArticlesRepositoryImpl(localDS,
    remoteDS)
    //When
    val testObserver = articlesRepo.getArticles().test()
    //Then
    testObserver.assertError(EmptyResultSetException::class.java)
    }
    

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28. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    https://www.rivu.dev/
    getArticles
    @Test
    fun `getArticles should emit both data`() {
    /* When both DS emits data
    * It should first emit localDS data and then from
    remoteDS */
    //Setup
    val dummyLocalData = TestDataFactory.dummyArticlesList
    val dummyRemoteData = TestDataFactory.dummyArticlesList
    val localDS = FakeSuccessDataStore(dummyLocalData)
    val remoteDS = FakeSuccessDataStore(dummyRemoteData)
    val articlesRepo = ArticlesRepositoryImpl(localDS,
    remoteDS)
    //When
    val testObserver = articlesRepo.getArticles().test()
    //Then
    testObserver.assertValueCount(2)
    testObserver.assertValues(dummyLocalData,
    dummyRemoteData)
    }
    

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29. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    ● Let them fail
    https://www.rivu.dev/
    

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30. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    ● Let them fail
    ● Write the code
    https://www.rivu.dev/
    class ArticlesRepositoryImpl (
    private val localDataStore: ArticlesDataStore,
    private val remoteDataStore: ArticlesDataStore
    ): ArticlesRepository {
    override fun fetchAndSyncArticles(): Single> {
    return remoteDataStore.getArticles()
    .flatMap {
    if (it.isNotEmpty()) {
    localDataStore.saveArticles(it)
    .andThen(Single.just(it))
    } else {
    Single.error(EmptyResultSetException(EMPTY_DATA_MESSAGE))
    }
    }
    }
    override fun getArticles(): Flowable> {
    return localDataStore.getArticles()
    .mergeWith(fetchAndSyncArticles())
    .onErrorResumeWith(fetchAndSyncArticles())
    }
    }
    

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31. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    ● Let them fail
    ● Write the code
    https://www.rivu.dev/
    class ArticlesRepositoryImpl (
    private val localDataStore: ArticlesDataStore,
    private val remoteDataStore: ArticlesDataStore
    ): ArticlesRepository {
    override fun fetchAndSyncArticles(): Single> {
    return remoteDataStore.getArticles()
    .flatMap {
    if (it.isNotEmpty()) {
    localDataStore.saveArticles(it)
    .andThen(Single.just(it))
    } else {
    Single.error(EmptyResultSetException(EMPTY_DATA_MESSAGE))
    }
    }
    }
    override fun getArticles(): Flowable> {
    return localDataStore.getArticles()
    .mergeWith(fetchAndSyncArticles())
    .onErrorResumeWith(fetchAndSyncArticles())
    }
    }
    

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32. Break down of
    Steps
    ● Create Interface
    ● Create Blank
    Implementation
    ● Write Tests
    ● Let them fail
    ● Write the code
    ● Run the tests again, see
    them pass 😎
    https://www.rivu.dev/
    

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33. Resources
    ● https://speakerdeck.com/rivuchk/android-worldwide-tdd-in-android this presentation
    ● http://agiledata.org/essays/tdd.html Intro to TDD
    ● https://www.raywenderlich.com/7109-test-driven-development-tutorial-for-android-getting-st
    arted TDD in Android Tutorial
    ● https://medium.com/mobility/how-to-do-tdd-in-android-90f013d91d7f TDD in Android
    Tutorial Series
    https://www.rivu.dev/
    

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34. Thanks!
    Rivu Chakraborty
    Twitter: @rivuchakraborty
    Website: https://rivu.dev
    

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