Apply flowOn(defaultDispatchers) for main-safe.

app/src/testDemo/kotlin/com/google/samples/apps/nowinandroid/ui/NiaAppStateTest.kt

@@ -24,6 +24,7 @@ import com.google.samples.apps.nowinandroid.core.navigation.NavigationState
 import com.google.samples.apps.nowinandroid.core.navigation.Navigator
 import com.google.samples.apps.nowinandroid.core.testing.repository.TestNewsRepository
 import com.google.samples.apps.nowinandroid.core.testing.repository.TestUserDataRepository
+import com.google.samples.apps.nowinandroid.core.testing.util.MainDispatcherRule
 import com.google.samples.apps.nowinandroid.core.testing.util.TestNetworkMonitor
 import com.google.samples.apps.nowinandroid.core.testing.util.TestTimeZoneMonitor
 import com.google.samples.apps.nowinandroid.feature.bookmarks.api.navigation.BookmarksNavKey
@@ -51,16 +52,19 @@ import kotlin.test.assertEquals
 @HiltAndroidTest
 class NiaAppStateTest {
 
-    @get:Rule
+    @get:Rule(0)
     val composeTestRule = createComposeRule()
 
+    @get:Rule(1)
+    val mainDispatcherRule = MainDispatcherRule()
+
     // Create the test dependencies.
     private val networkMonitor = TestNetworkMonitor()
 
     private val timeZoneMonitor = TestTimeZoneMonitor()
 
     private val userNewsResourceRepository =
-        CompositeUserNewsResourceRepository(TestNewsRepository(), TestUserDataRepository())
+        CompositeUserNewsResourceRepository(TestNewsRepository(), TestUserDataRepository(), mainDispatcherRule.testDispatcher)
 
     // Subject under test.
     private lateinit var state: NiaAppState

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/CompositeUserNewsResourceRepository.kt

@@ -18,11 +18,15 @@ package com.google.samples.apps.nowinandroid.core.data.repository
 
 import com.google.samples.apps.nowinandroid.core.model.data.UserNewsResource
 import com.google.samples.apps.nowinandroid.core.model.data.mapToUserNewsResources
+import com.google.samples.apps.nowinandroid.core.network.Dispatcher
+import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.Default
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
 import javax.inject.Inject
 
@@ -33,8 +37,8 @@ import javax.inject.Inject
 class CompositeUserNewsResourceRepository @Inject constructor(
     val newsRepository: NewsRepository,
     val userDataRepository: UserDataRepository,
+    @Dispatcher(Default) private val defaultDispatcher: CoroutineDispatcher,
 ) : UserNewsResourceRepository {
-
     /**
      * Returns available news resources (joined with user data) matching the given query.
      */
@@ -44,7 +48,7 @@ class CompositeUserNewsResourceRepository @Inject constructor(
         newsRepository.getNewsResources(query)
             .combine(userDataRepository.userData) { newsResources, userData ->
                 newsResources.mapToUserNewsResources(userData)
-            }
+            }.flowOn(defaultDispatcher)
 
     /**
      * Returns available news resources (joined with user data) for the followed topics.

core/data/src/main/kotlin/com/google/samples/apps/nowinandroid/core/data/repository/DefaultSearchContentsRepository.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.core.data.repository
 
+import androidx.tracing.trace
 import com.google.samples.apps.nowinandroid.core.database.dao.NewsResourceDao
 import com.google.samples.apps.nowinandroid.core.database.dao.NewsResourceFtsDao
 import com.google.samples.apps.nowinandroid.core.database.dao.TopicDao
@@ -25,13 +26,15 @@ import com.google.samples.apps.nowinandroid.core.database.model.asExternalModel
 import com.google.samples.apps.nowinandroid.core.database.model.asFtsEntity
 import com.google.samples.apps.nowinandroid.core.model.data.SearchResult
 import com.google.samples.apps.nowinandroid.core.network.Dispatcher
+import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.Default
 import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.IO
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.mapLatest
 import kotlinx.coroutines.withContext
 import javax.inject.Inject
@@ -42,6 +45,7 @@ internal class DefaultSearchContentsRepository @Inject constructor(
     private val topicDao: TopicDao,
     private val topicFtsDao: TopicFtsDao,
     @Dispatcher(IO) private val ioDispatcher: CoroutineDispatcher,
+    @Dispatcher(Default) private val defaultDispatcher: CoroutineDispatcher,
 ) : SearchContentsRepository {
 
     override suspend fun populateFtsData() {
@@ -75,18 +79,22 @@ internal class DefaultSearchContentsRepository @Inject constructor(
             .distinctUntilChanged()
             .flatMapLatest(topicDao::getTopicEntities)
         return combine(newsResourcesFlow, topicsFlow) { newsResources, topics ->
-            SearchResult(
-                topics = topics.map { it.asExternalModel() },
-                newsResources = newsResources.map { it.asExternalModel() },
-            )
-        }
+            trace("DefaultSearchContentsRepository.searchContents") {
+                SearchResult(
+                    topics = topics.map { it.asExternalModel() },
+                    newsResources = newsResources.map { it.asExternalModel() },
+                )
+            }
+        }.flowOn(defaultDispatcher)
     }
 
     override fun getSearchContentsCount(): Flow<Int> =
         combine(
             newsResourceFtsDao.getCount(),
             topicFtsDao.getCount(),
         ) { newsResourceCount, topicsCount ->
-            newsResourceCount + topicsCount
-        }
+            trace("DefaultSearchContentsRepository.getSearchContentsCount") {
+                newsResourceCount + topicsCount
+            }
+        }.flowOn(defaultDispatcher)
 }

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/CompositeUserNewsResourceRepositoryTest.kt

@@ -24,20 +24,26 @@ import com.google.samples.apps.nowinandroid.core.model.data.mapToUserNewsResourc
 import com.google.samples.apps.nowinandroid.core.testing.repository.TestNewsRepository
 import com.google.samples.apps.nowinandroid.core.testing.repository.TestUserDataRepository
 import com.google.samples.apps.nowinandroid.core.testing.repository.emptyUserData
+import com.google.samples.apps.nowinandroid.core.testing.util.MainDispatcherRule
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
 import kotlinx.datetime.Instant
+import org.junit.Rule
 import org.junit.Test
 import kotlin.test.assertEquals
 
 class CompositeUserNewsResourceRepositoryTest {
 
+    @get:Rule
+    val dispatcherRule = MainDispatcherRule()
+
     private val newsRepository = TestNewsRepository()
     private val userDataRepository = TestUserDataRepository()
 
     private val userNewsResourceRepository = CompositeUserNewsResourceRepository(
         newsRepository = newsRepository,
         userDataRepository = userDataRepository,
+        defaultDispatcher = dispatcherRule.testDispatcher,
     )
 
     @Test

core/domain/src/main/kotlin/com/google/samples/apps/nowinandroid/core/domain/GetFollowableTopicsUseCase.kt

@@ -16,13 +16,18 @@
 
 package com.google.samples.apps.nowinandroid.core.domain
 
+import androidx.tracing.trace
 import com.google.samples.apps.nowinandroid.core.data.repository.TopicsRepository
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
 import com.google.samples.apps.nowinandroid.core.domain.TopicSortField.NAME
 import com.google.samples.apps.nowinandroid.core.domain.TopicSortField.NONE
 import com.google.samples.apps.nowinandroid.core.model.data.FollowableTopic
+import com.google.samples.apps.nowinandroid.core.network.Dispatcher
+import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.Default
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.flowOn
 import javax.inject.Inject
 
 /**
@@ -31,6 +36,7 @@ import javax.inject.Inject
 class GetFollowableTopicsUseCase @Inject constructor(
     private val topicsRepository: TopicsRepository,
     private val userDataRepository: UserDataRepository,
+    @Dispatcher(Default) private val defaultDispatcher: CoroutineDispatcher,
 ) {
     /**
      * Returns a list of topics with their associated followed state.
@@ -41,18 +47,20 @@ class GetFollowableTopicsUseCase @Inject constructor(
         userDataRepository.userData,
         topicsRepository.getTopics(),
     ) { userData, topics ->
-        val followedTopics = topics
-            .map { topic ->
-                FollowableTopic(
-                    topic = topic,
-                    isFollowed = topic.id in userData.followedTopics,
-                )
+        trace("GetFollowableTopicsUseCase.invoke") {
+            val followedTopics = topics
+                .map { topic ->
+                    FollowableTopic(
+                        topic = topic,
+                        isFollowed = topic.id in userData.followedTopics,
+                    )
+                }
+            when (sortBy) {
+                NAME -> followedTopics.sortedBy { it.topic.name }
+                else -> followedTopics
             }
-        when (sortBy) {
-            NAME -> followedTopics.sortedBy { it.topic.name }
-            else -> followedTopics
         }
-    }
+    }.flowOn(defaultDispatcher)
 }
 
 enum class TopicSortField {

core/domain/src/main/kotlin/com/google/samples/apps/nowinandroid/core/domain/GetSearchContentsUseCase.kt

@@ -23,8 +23,12 @@ import com.google.samples.apps.nowinandroid.core.model.data.SearchResult
 import com.google.samples.apps.nowinandroid.core.model.data.UserData
 import com.google.samples.apps.nowinandroid.core.model.data.UserNewsResource
 import com.google.samples.apps.nowinandroid.core.model.data.UserSearchResult
+import com.google.samples.apps.nowinandroid.core.network.Dispatcher
+import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.Default
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.flowOn
 import javax.inject.Inject
 
 /**
@@ -33,16 +37,20 @@ import javax.inject.Inject
 class GetSearchContentsUseCase @Inject constructor(
     private val searchContentsRepository: SearchContentsRepository,
     private val userDataRepository: UserDataRepository,
+    @Dispatcher(Default) private val defaultDispatcher: CoroutineDispatcher,
 ) {
 
     operator fun invoke(
         searchQuery: String,
     ): Flow<UserSearchResult> =
         searchContentsRepository.searchContents(searchQuery)
-            .mapToUserSearchResult(userDataRepository.userData)
+            .mapToUserSearchResult(userDataRepository.userData, defaultDispatcher)
 }
 
-private fun Flow<SearchResult>.mapToUserSearchResult(userDataStream: Flow<UserData>): Flow<UserSearchResult> =
+private fun Flow<SearchResult>.mapToUserSearchResult(
+    userDataStream: Flow<UserData>,
+    defaultDispatcher: CoroutineDispatcher,
+): Flow<UserSearchResult> =
     combine(userDataStream) { searchResult, userData ->
         UserSearchResult(
             topics = searchResult.topics.map { topic ->
@@ -58,4 +66,4 @@ private fun Flow<SearchResult>.mapToUserSearchResult(userDataStream: Flow<UserDa
                 )
             },
         )
-    }
+    }.flowOn(defaultDispatcher)

core/domain/src/test/kotlin/com/google/samples/apps/nowinandroid/core/domain/GetFollowableTopicsUseCaseTest.kt

@@ -39,6 +39,7 @@ class GetFollowableTopicsUseCaseTest {
     val useCase = GetFollowableTopicsUseCase(
         topicsRepository,
         userDataRepository,
+        mainDispatcherRule.testDispatcher,
     )
 
     @Test

core/testing/src/main/kotlin/com/google/samples/apps/nowinandroid/core/testing/util/MainDispatcherRule.kt

@@ -30,7 +30,11 @@ import org.junit.runner.Description
  * for the duration of the test.
  */
 class MainDispatcherRule(
-    private val testDispatcher: TestDispatcher = UnconfinedTestDispatcher(),
+    /**
+     * Expose testDispatcher to share the scheduler to the test.
+     * See more in [Documentation](https://developer.android.com/kotlin/coroutines/test#injecting-test-dispatchers)
+     */
+    val testDispatcher: TestDispatcher = UnconfinedTestDispatcher(),
 ) : TestWatcher() {
     override fun starting(description: Description) = Dispatchers.setMain(testDispatcher)
 

feature/bookmarks/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/BookmarksViewModelTest.kt

@@ -49,6 +49,7 @@ class BookmarksViewModelTest {
     private val userNewsResourceRepository = CompositeUserNewsResourceRepository(
         newsRepository = newsRepository,
         userDataRepository = userDataRepository,
+        dispatcherRule.testDispatcher,
     )
     private lateinit var viewModel: BookmarksViewModel
 

feature/foryou/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/feature/foryou/impl/ForYouViewModelTest.kt

@@ -65,11 +65,13 @@ class ForYouViewModelTest {
     private val userNewsResourceRepository = CompositeUserNewsResourceRepository(
         newsRepository = newsRepository,
         userDataRepository = userDataRepository,
+        defaultDispatcher = mainDispatcherRule.testDispatcher,
     )
 
     private val getFollowableTopicsUseCase = GetFollowableTopicsUseCase(
         topicsRepository = topicsRepository,
         userDataRepository = userDataRepository,
+        defaultDispatcher = mainDispatcherRule.testDispatcher,
     )
 
     private val savedStateHandle = SavedStateHandle()

feature/interests/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/interests/impl/InterestsViewModelTest.kt

@@ -61,6 +61,7 @@ class InterestsViewModelTest {
     private val getFollowableTopicsUseCase = GetFollowableTopicsUseCase(
         topicsRepository = topicsRepository,
         userDataRepository = userDataRepository,
+        defaultDispatcher = mainDispatcherRule.testDispatcher,
     )
     private lateinit var viewModel: InterestsViewModel
 

feature/search/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/feature/search/impl/SearchViewModelTest.kt

@@ -57,6 +57,7 @@ class SearchViewModelTest {
     private val getSearchContentsUseCase = GetSearchContentsUseCase(
         searchContentsRepository = searchContentsRepository,
         userDataRepository = userDataRepository,
+        dispatcherRule.testDispatcher,
     )
     private val recentSearchRepository = TestRecentSearchRepository()
     private val getRecentQueryUseCase = GetRecentSearchQueriesUseCase(recentSearchRepository)

feature/topic/impl/src/test/kotlin/com/google/samples/apps/nowinandroid/feature/topic/impl/TopicViewModelTest.kt

@@ -52,6 +52,7 @@ class TopicViewModelTest {
     private val userNewsResourceRepository = CompositeUserNewsResourceRepository(
         newsRepository = newsRepository,
         userDataRepository = userDataRepository,
+        defaultDispatcher = dispatcherRule.testDispatcher,
     )
     private lateinit var viewModel: TopicViewModel