Add additional tests to PagingWithNetworkSample

PagingWithNetworkSample/app/build.gradle

@@ -89,6 +89,7 @@ dependencies {
     androidTestImplementation deps.atsl.rules
     androidTestImplementation deps.arch_core.testing
     androidTestImplementation deps.espresso.contrib
+    androidTestImplementation deps.coroutines.test
 
     testImplementation deps.junit
     testImplementation deps.coroutines.test

PagingWithNetworkSample/app/src/androidTest/java/com/android/example/paging/pagingwithnetwork/reddit/ui/PageKeyedRemoteMediatorTest.kt

@@ -0,0 +1,108 @@
+package com.android.example.paging.pagingwithnetwork.reddit.ui
+
+import androidx.paging.ExperimentalPagingApi
+import androidx.paging.LoadType
+import androidx.paging.PagingConfig
+import androidx.paging.PagingState
+import androidx.paging.RemoteMediator
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.android.example.paging.pagingwithnetwork.reddit.db.RedditDb
+import com.android.example.paging.pagingwithnetwork.reddit.repository.inDb.PageKeyedRemoteMediator
+import com.android.example.paging.pagingwithnetwork.reddit.vo.RedditPost
+import com.android.example.paging.pagingwithnetwork.repository.FakeRedditApi
+import com.android.example.paging.pagingwithnetwork.repository.PostFactory
+import junit.framework.Assert.assertFalse
+import junit.framework.Assert.assertTrue
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.runTest
+import org.junit.After
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@ExperimentalPagingApi
+@OptIn(ExperimentalCoroutinesApi::class)
+@RunWith(AndroidJUnit4::class)
+class PageKeyedRemoteMediatorTest {
+    private val postFactory = PostFactory()
+    private val mockPosts = listOf(
+        postFactory.createRedditPost(SubRedditViewModel.DEFAULT_SUBREDDIT),
+        postFactory.createRedditPost(SubRedditViewModel.DEFAULT_SUBREDDIT),
+        postFactory.createRedditPost(SubRedditViewModel.DEFAULT_SUBREDDIT)
+    )
+    private val mockApi = FakeRedditApi()
+
+    private val mockDb = RedditDb.create(
+        ApplicationProvider.getApplicationContext(),
+        useInMemory = true
+    )
+
+    @After
+    fun tearDown() {
+        mockDb.clearAllTables()
+        // Clear out failure message to default to the successful response.
+        mockApi.failureMsg = null
+        // Clear out posts after each test run.
+        mockApi.clearPosts()
+    }
+
+    @Test
+    fun refreshLoadReturnsSuccessResultWhenMoreDataIsPresent() = runTest {
+        // Add mock results for the API to return.
+        mockPosts.forEach { post -> mockApi.addPost(post) }
+        val remoteMediator = PageKeyedRemoteMediator(
+            mockDb,
+            mockApi,
+            SubRedditViewModel.DEFAULT_SUBREDDIT
+        )
+        val pagingState = PagingState<Int, RedditPost>(
+            listOf(),
+            null,
+            PagingConfig(10),
+            10
+        )
+        val result = remoteMediator.load(LoadType.REFRESH, pagingState)
+        assertTrue(result is RemoteMediator.MediatorResult.Success)
+        assertFalse((result as RemoteMediator.MediatorResult.Success).endOfPaginationReached)
+    }
+
+    @Test
+    fun refreshLoadSuccessAndEndOfPaginationWhenNoMoreData() = runTest {
+        // To test endOfPaginationReached, don't set up the mockApi to return post
+        // data here.
+        val remoteMediator = PageKeyedRemoteMediator(
+            mockDb,
+            mockApi,
+            SubRedditViewModel.DEFAULT_SUBREDDIT
+        )
+        val pagingState = PagingState<Int, RedditPost>(
+            listOf(),
+            null,
+            PagingConfig(10),
+            10
+        )
+        val result = remoteMediator.load(LoadType.REFRESH, pagingState)
+        assertTrue(result is RemoteMediator.MediatorResult.Success)
+        assertTrue((result as RemoteMediator.MediatorResult.Success).endOfPaginationReached)
+    }
+
+    @Test
+    fun refreshLoadReturnsErrorResultWhenErrorOccurs() = runTest {
+        // Set up failure message to throw exception from the mock API.
+        mockApi.failureMsg = "Throw test failure"
+        val remoteMediator = PageKeyedRemoteMediator(
+            mockDb,
+            mockApi,
+            SubRedditViewModel.DEFAULT_SUBREDDIT
+        )
+        val pagingState = PagingState<Int, RedditPost>(
+            listOf(),
+            null,
+            PagingConfig(10),
+            10
+        )
+        val result = remoteMediator.load(LoadType.REFRESH, pagingState)
+        assertTrue(result is RemoteMediator.MediatorResult.Error)
+    }
+
+}

PagingWithNetworkSample/app/src/androidTest/java/com/android/example/paging/pagingwithnetwork/reddit/ui/PagingDataTransformTest.kt

@@ -0,0 +1,79 @@
+package com.android.example.paging.pagingwithnetwork.reddit.ui
+
+import androidx.paging.AsyncPagingDataDiffer
+import androidx.paging.PagingData
+import androidx.paging.filter
+import androidx.paging.map
+import androidx.recyclerview.widget.DiffUtil
+import androidx.recyclerview.widget.ListUpdateCallback
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+
+@ExperimentalCoroutinesApi
+class PagingDataTransformTest {
+    private val testScope = TestScope()
+    private val testDispatcher = StandardTestDispatcher(testScope.testScheduler)
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(testDispatcher)
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain()
+    }
+
+    @Test
+    fun differTransformsData() = testScope.runTest {
+        val data = PagingData.from(listOf(1, 2, 3, 4)).myHelperTransformFunction()
+        val differ = AsyncPagingDataDiffer(
+            diffCallback = MyDiffCallback(),
+            updateCallback = NoopListCallback(),
+            workerDispatcher = Dispatchers.Main
+        )
+
+        // You don't need to use lifecycleScope.launch() if you're using
+        // PagingData.from()
+        differ.submitData(data)
+
+        // Wait for transforms and the differ to process all updates.
+        advanceUntilIdle()
+        assertEquals(listOf(4, 16), differ.snapshot().items)
+    }
+}
+
+fun PagingData<Int>.myHelperTransformFunction(): PagingData<Int> {
+    return this.map { item ->
+        item * item
+    }.filter { item ->
+        item % 2 == 0
+    }
+}
+
+class NoopListCallback : ListUpdateCallback {
+    override fun onChanged(position: Int, count: Int, payload: Any?) {}
+    override fun onMoved(fromPosition: Int, toPosition: Int) {}
+    override fun onInserted(position: Int, count: Int) {}
+    override fun onRemoved(position: Int, count: Int) {}
+}
+
+class MyDiffCallback : DiffUtil.ItemCallback<Int>() {
+    override fun areItemsTheSame(oldItem: Int, newItem: Int): Boolean {
+        return oldItem == newItem
+    }
+
+    override fun areContentsTheSame(oldItem: Int, newItem: Int): Boolean {
+        return oldItem == newItem
+    }
+}

PagingWithNetworkSample/app/src/test-common/java/com/android/example/paging/pagingwithnetwork/repository/FakeRedditApi.kt

@@ -37,6 +37,10 @@ class FakeRedditApi : RedditApi {
         subreddit.items.add(post)
     }
 
+    fun clearPosts() {
+        model.clear()
+    }
+
     private fun findPosts(
         subreddit: String,
         limit: Int,