Migrate from RxJava to Kotlin Flow

steliosfran · steliosfran · commit 22fd588205cb · 2023-10-10T00:04:29.000+03:00
diff --git a/README.md b/README.md
@@ -11,12 +11,14 @@ For a comprehensive guide on how to follow this methodology, please refer to the
 ## Setup
 
 1. Clone the repository
-2. Examine the structure of the tests in the `ChatViewModelSpec.kt` file.
+2. Checkout the `main` branch for Kotlin Flow or `rxjava` for RxJava
+3. Examine the structure of the tests in the `ChatViewModelSpec.kt` file.
 
 ## Libraries Used
 
 - Dependency Injection: [Koin](https://github.com/InsertKoinIO/koin)
 - Testing Framework: [Kotest](https://github.com/kotest/kotest)
+- Reactive Framework: Both [Kotlin Flow](https://github.com/Kotlin/kotlinx.coroutines) and [RxJava](https://github.com/ReactiveX/RxJava) are supported
 
 ## Contact
 
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
@@ -77,6 +77,7 @@ dependencies {
     testImplementation(libs.rxjava)
     testImplementation(platform(libs.junit.jupiter.bom))
     testImplementation(libs.junit.jupiter.api)
+    testImplementation(libs.kotlinx.coroutines.test)
 
     testRuntimeOnly(libs.junit.jupiter.engine)
 
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/common/CoroutineDispatcherProvider.kt b/app/src/main/java/com/steliosf/unittestingdiet/common/CoroutineDispatcherProvider.kt
@@ -0,0 +1,7 @@
+package com.steliosf.unittestingdiet.common
+
+import kotlinx.coroutines.CoroutineDispatcher
+
+interface CoroutineDispatcherProvider {
+    val main: CoroutineDispatcher
+}
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/common/DefaultCoroutineDispatcherProvider.kt b/app/src/main/java/com/steliosf/unittestingdiet/common/DefaultCoroutineDispatcherProvider.kt
@@ -0,0 +1,8 @@
+package com.steliosf.unittestingdiet.common
+
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Dispatchers
+
+class DefaultCoroutineDispatcherProvider : CoroutineDispatcherProvider {
+    override val main: CoroutineDispatcher = Dispatchers.Main
+}
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/data/datasource/ChatDataSource.kt b/app/src/main/java/com/steliosf/unittestingdiet/data/datasource/ChatDataSource.kt
@@ -2,10 +2,8 @@ package com.steliosf.unittestingdiet.data.datasource
 
 import com.steliosf.unittestingdiet.domain.model.Message
 import com.steliosf.unittestingdiet.domain.model.User
-import io.reactivex.rxjava3.core.Completable
-import io.reactivex.rxjava3.core.Single
 
 interface ChatDataSource {
-    fun getChatMessages(user: User): Single<List<Message>>
-    fun sendChatMessage(message: Message, user: User): Completable
+    suspend fun getChatMessages(user: User): List<Message>
+    suspend fun sendChatMessage(message: Message, user: User)
 }
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/data/repository/ChatMessagesRepository.kt b/app/src/main/java/com/steliosf/unittestingdiet/data/repository/ChatMessagesRepository.kt
@@ -3,37 +3,25 @@ package com.steliosf.unittestingdiet.data.repository
 import com.steliosf.unittestingdiet.data.datasource.ChatDataSource
 import com.steliosf.unittestingdiet.domain.model.Message
 import com.steliosf.unittestingdiet.domain.model.User
-import io.reactivex.rxjava3.core.Completable
-import io.reactivex.rxjava3.core.Observable
-import io.reactivex.rxjava3.subjects.BehaviorSubject
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.emitAll
+import kotlinx.coroutines.flow.flow
 
 class ChatMessagesRepository(
     private val chatDataSource: ChatDataSource
 ) {
+    private val _cachedChatMessages = MutableStateFlow<List<Message>>(emptyList())
 
-    private val cachedChatMessages: BehaviorSubject<List<Message>> = BehaviorSubject.create()
-
-    fun getChatMessages(user: User): Observable<List<Message>> {
-        return if (cachedChatMessages.hasValue()) cachedChatMessages else {
-            loadExistingChatMessages(user).andThen(cachedChatMessages)
+    fun getChatMessages(user: User): Flow<List<Message>> = flow {
+        if (_cachedChatMessages.value.isEmpty()) {
+            _cachedChatMessages.emit(chatDataSource.getChatMessages(user))
         }
+        emitAll(_cachedChatMessages)
     }
 
-    fun sendChatMessage(message: Message, user: User): Completable {
-        return chatDataSource.sendChatMessage(message, user)
-            .doOnSubscribe {
-                cachedChatMessages.onNext(getCurrentMessagesList() + message)
-            }.doOnComplete { /* .. */ }
-    }
-
-    private fun loadExistingChatMessages(user: User): Completable {
-        return chatDataSource.getChatMessages(user)
-            .doOnSuccess {
-                cachedChatMessages.onNext(it)
-            }.ignoreElement()
-    }
-
-    private fun getCurrentMessagesList(): List<Message> {
-        return cachedChatMessages.value ?: emptyList()
+    suspend fun sendChatMessage(message: Message, user: User) {
+        _cachedChatMessages.apply { value = value + message }
+        chatDataSource.sendChatMessage(message, user)
     }
 }
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/di/AppModule.kt b/app/src/main/java/com/steliosf/unittestingdiet/di/AppModule.kt
@@ -1,5 +1,7 @@
 package com.steliosf.unittestingdiet.di
 
+import com.steliosf.unittestingdiet.common.CoroutineDispatcherProvider
+import com.steliosf.unittestingdiet.common.DefaultCoroutineDispatcherProvider
 import com.steliosf.unittestingdiet.data.repository.ChatMessagesRepository
 import com.steliosf.unittestingdiet.domain.usecase.GetChatMessagesUseCase
 import com.steliosf.unittestingdiet.domain.usecase.SendTextMessageUseCase
@@ -14,6 +16,7 @@ val appModule = module {
 
     factoryOf(::GetChatMessagesUseCase)
     factoryOf(::SendTextMessageUseCase)
+    factoryOf<CoroutineDispatcherProvider>(::DefaultCoroutineDispatcherProvider)
 
     singleOf(::ChatMessagesRepository)
 }
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/domain/usecase/GetChatMessagesUseCase.kt b/app/src/main/java/com/steliosf/unittestingdiet/domain/usecase/GetChatMessagesUseCase.kt
@@ -3,13 +3,14 @@ package com.steliosf.unittestingdiet.domain.usecase
 import com.steliosf.unittestingdiet.data.repository.ChatMessagesRepository
 import com.steliosf.unittestingdiet.domain.model.Message
 import com.steliosf.unittestingdiet.domain.model.User
-import io.reactivex.rxjava3.core.Observable
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
 
 class GetChatMessagesUseCase(
     private val chatMessagesRepository: ChatMessagesRepository
 ) {
 
-    operator fun invoke(user: User): Observable<List<Message>> {
+    operator fun invoke(user: User): Flow<List<Message>> {
         return chatMessagesRepository.getChatMessages(user).map { messagesList ->
             messagesList.sortedBy { it.date.time }
         }
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/domain/usecase/SendTextMessageUseCase.kt b/app/src/main/java/com/steliosf/unittestingdiet/domain/usecase/SendTextMessageUseCase.kt
@@ -1,21 +1,20 @@
 package com.steliosf.unittestingdiet.domain.usecase
 
-import com.steliosf.unittestingdiet.domain.model.User
-import com.steliosf.unittestingdiet.domain.model.error.InvalidMessageException
 import com.steliosf.unittestingdiet.data.repository.ChatMessagesRepository
 import com.steliosf.unittestingdiet.domain.factory.MessageFactory
-import io.reactivex.rxjava3.core.Completable
+import com.steliosf.unittestingdiet.domain.model.User
+import com.steliosf.unittestingdiet.domain.model.error.InvalidMessageException
 
 class SendTextMessageUseCase(
     private val chatMessagesRepository: ChatMessagesRepository
 ) {
 
-    operator fun invoke(text: String, user: User): Completable {
-        return if (isValid(text)) {
+    suspend operator fun invoke(text: String, user: User) {
+        if (isValid(text)) {
             val message = MessageFactory.fromText(text)
             chatMessagesRepository.sendChatMessage(message, user)
         } else {
-            Completable.error(InvalidMessageException("Message is too long"))
+            throw InvalidMessageException("Message is too long")
         }
     }
 
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/presentation/viewmodel/BaseViewModel.kt b/app/src/main/java/com/steliosf/unittestingdiet/presentation/viewmodel/BaseViewModel.kt
diff --git a/app/src/main/java/com/steliosf/unittestingdiet/presentation/viewmodel/ChatViewModel.kt b/app/src/main/java/com/steliosf/unittestingdiet/presentation/viewmodel/ChatViewModel.kt
@@ -1,29 +1,44 @@
 package com.steliosf.unittestingdiet.presentation.viewmodel
 
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.steliosf.unittestingdiet.common.CoroutineDispatcherProvider
 import com.steliosf.unittestingdiet.domain.model.User
-import com.steliosf.unittestingdiet.presentation.ui.model.MessageUiModel
 import com.steliosf.unittestingdiet.domain.usecase.GetChatMessagesUseCase
 import com.steliosf.unittestingdiet.domain.usecase.SendTextMessageUseCase
 import com.steliosf.unittestingdiet.presentation.ui.mapper.MessageUiModelMapper
-import io.reactivex.rxjava3.core.Observable
+import com.steliosf.unittestingdiet.presentation.ui.model.MessageUiModel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.launch
 
 class ChatViewModel(
     private val getChatMessagesUseCase: GetChatMessagesUseCase,
     private val sendTextMessageUseCase: SendTextMessageUseCase,
-    private val user: User
-) : BaseViewModel() {
+    private val user: User,
+    private val coroutineDispatcherProvider: CoroutineDispatcherProvider
+) : ViewModel() {
 
     data class State(
         val messages: List<MessageUiModel>
     )
 
-    val state: Observable<State>
-        get() = getChatMessagesUseCase(user).map {
-            val messageUiModelList = MessageUiModelMapper.fromMessagesList(it)
-            State(messageUiModelList)
+    private val _state = MutableStateFlow(State(emptyList()))
+    val state: StateFlow<State> = _state.asStateFlow()
+
+    init {
+        viewModelScope.launch(coroutineDispatcherProvider.main) {
+            getChatMessagesUseCase(user).map {
+                State(MessageUiModelMapper.fromMessagesList(it))
+            }.collect { newState ->
+                _state.value = newState
+            }
         }
+    }
 
-    fun onTextMessageSent(text: String) {
-        sendTextMessageUseCase(text, user).safeSubscribe()
+    fun onTextMessageSent(text: String) = viewModelScope.launch(coroutineDispatcherProvider.main) {
+        sendTextMessageUseCase(text, user)
     }
 }
diff --git a/app/src/test/java/com/steliosf/unittestingdiet/fixtures/common/TestCoroutineDispatcherProvider.kt b/app/src/test/java/com/steliosf/unittestingdiet/fixtures/common/TestCoroutineDispatcherProvider.kt
@@ -0,0 +1,9 @@
+package com.steliosf.unittestingdiet.fixtures.common
+
+import com.steliosf.unittestingdiet.common.CoroutineDispatcherProvider
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.test.TestCoroutineDispatcher
+
+class TestCoroutineDispatcherProvider : CoroutineDispatcherProvider {
+    override val main: CoroutineDispatcher = TestCoroutineDispatcher()
+}
diff --git a/app/src/test/java/com/steliosf/unittestingdiet/fixtures/datasource/FakeChatDataSource.kt b/app/src/test/java/com/steliosf/unittestingdiet/fixtures/datasource/FakeChatDataSource.kt
@@ -3,20 +3,16 @@ package com.steliosf.unittestingdiet.fixtures.datasource
 import com.steliosf.unittestingdiet.data.datasource.ChatDataSource
 import com.steliosf.unittestingdiet.domain.model.Message
 import com.steliosf.unittestingdiet.domain.model.User
-import io.reactivex.rxjava3.core.Completable
-import io.reactivex.rxjava3.core.Single
 
 class FakeChatDataSource : ChatDataSource {
     private var messagesList = mutableListOf<Message>()
 
-    override fun getChatMessages(user: User): Single<List<Message>> {
-        return Single.just(messagesList)
+    override suspend fun getChatMessages(user: User): List<Message> {
+        return messagesList
     }
 
-    override fun sendChatMessage(message: Message, user: User): Completable {
-        return Completable.fromCallable {
-            messagesList.add(message)
-        }
+    override suspend fun sendChatMessage(message: Message, user: User) {
+        messagesList.add(message)
     }
 
     fun setResponse(messagesList: List<Message>) {
diff --git a/app/src/test/java/com/steliosf/unittestingdiet/fixtures/di/TestsModule.kt b/app/src/test/java/com/steliosf/unittestingdiet/fixtures/di/TestsModule.kt
@@ -1,11 +1,15 @@
 package com.steliosf.unittestingdiet.fixtures.di
 
+import com.steliosf.unittestingdiet.common.CoroutineDispatcherProvider
 import com.steliosf.unittestingdiet.data.datasource.ChatDataSource
+import com.steliosf.unittestingdiet.fixtures.common.TestCoroutineDispatcherProvider
 import com.steliosf.unittestingdiet.fixtures.datasource.FakeChatDataSource
+import org.koin.core.module.dsl.factoryOf
 import org.koin.core.module.dsl.singleOf
 import org.koin.dsl.bind
 import org.koin.dsl.module
 
-val fakeChatDataSourceModule = module {
+val testsModule = module {
     singleOf(::FakeChatDataSource) bind ChatDataSource::class
+    factoryOf<CoroutineDispatcherProvider>(::TestCoroutineDispatcherProvider)
 }
diff --git a/app/src/test/java/com/steliosf/unittestingdiet/viewmodel/BaseBehaviorSpec.kt b/app/src/test/java/com/steliosf/unittestingdiet/viewmodel/BaseBehaviorSpec.kt
@@ -1,7 +1,7 @@
 package com.steliosf.unittestingdiet.viewmodel
 
 import com.steliosf.unittestingdiet.di.appModule
-import com.steliosf.unittestingdiet.fixtures.di.fakeChatDataSourceModule
+import com.steliosf.unittestingdiet.fixtures.di.testsModule
 import io.kotest.core.spec.IsolationMode
 import io.kotest.core.spec.Spec
 import io.kotest.core.spec.style.BehaviorSpec
@@ -12,7 +12,7 @@ import org.koin.test.KoinTest
 
 open class BaseBehaviorSpec : BehaviorSpec(), KoinTest {
 
-    private val modulesToLoad: List<Module> = appModule + fakeChatDataSourceModule
+    private val modulesToLoad: List<Module> = appModule + testsModule
 
     override fun isolationMode() = IsolationMode.InstancePerLeaf
 
diff --git a/app/src/test/java/com/steliosf/unittestingdiet/viewmodel/ChatViewModelSpec.kt b/app/src/test/java/com/steliosf/unittestingdiet/viewmodel/ChatViewModelSpec.kt
@@ -24,10 +24,9 @@ class ChatViewModelSpec : BaseBehaviorSpec() {
         beforeSpec { fakeDataSourceResponse() }
 
         Given("I am in chat") {
-            val stateObserver = viewModel.state.test()
 
             Then("The existing messages are displayed") {
-                stateObserver.values().last() shouldBeEqual ChatViewModel.State(
+                viewModel.state.value shouldBeEqual ChatViewModel.State(
                     messages = listOf(
                         MessageUiModel(
                             text = "1st message",
@@ -47,7 +46,7 @@ class ChatViewModelSpec : BaseBehaviorSpec() {
                     textMessage = "2nd message"
 
                     Then("It is displayed") {
-                        stateObserver.values().last() shouldBeEqual ChatViewModel.State(
+                        viewModel.state.value shouldBeEqual ChatViewModel.State(
                             messages = listOf(
                                 MessageUiModel(
                                     text = "1st message",
@@ -66,7 +65,7 @@ class ChatViewModelSpec : BaseBehaviorSpec() {
                     textMessage = (1..180).joinToString("") { "a" }
 
                     Then("It is not displayed") {
-                        stateObserver.values().last() shouldBeEqual ChatViewModel.State(
+                        viewModel.state.value shouldBeEqual ChatViewModel.State(
                             messages = listOf(
                                 MessageUiModel(
                                     "1st message",
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
@@ -9,6 +9,7 @@ rxjava = "3.1.8"
 koin-bom = "3.5.1"
 kotest-bom = "5.7.2"
 junit-bom = "5.9.3"
+kotlinx-coroutines-test = "1.7.0"
 
 [libraries]
 core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "core-ktx" }
@@ -31,6 +32,7 @@ rxjava = { module = "io.reactivex.rxjava3:rxjava", version.ref = "rxjava" }
 junit-jupiter-bom = { module = "org.junit:junit-bom", version.ref = "junit-bom" }
 junit-jupiter-api = { module = "org.junit.jupiter:junit-jupiter-api" }
 junit-jupiter-engine = { module = "org.junit.jupiter:junit-jupiter-engine" }
+kotlinx-coroutines-test = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-test", version.ref = "kotlinx-coroutines-test" }
 
 [plugins]
 com-android-application = { id = "com.android.application", version.ref = "agp" }
