测试 Paging 实现 (View)

概念和 Jetpack Compose 实现

在应用中实现 Paging 库需要辅以稳健的测试策略。您应测试 PagingSource 和 RemoteMediator 等数据加载组件，以确保这些组件按预期运行。您还应编写端到端测试，以验证 Paging 实现中的所有组件能否正确协作，而不产生意外的副效应。

本指南将介绍如何在应用的数据层中测试 Paging 库，以及如何为整个 Paging 实现编写端到端测试。

数据层测试

为数据层中的组件编写单元测试，以确保这些组件能从数据源正确加载数据。提供依赖项的虚假版本，以验证被测组件能否在单独运行时正常工作。您需要在代码库层中测试的组件之一是 RemoteMediator。

`RemoteMediator` 测试

RemoteMediator 单元测试的目的是验证 load() 函数是否会返回正确的 MediatorResult。副效应测试（例如将数据插入数据库）更适合集成测试。

第一步是确定 RemoteMediator 实现需要的依赖项。以下示例演示了需要 Room 数据库、Retrofit 接口和搜索字符串的 RemoteMediator 实现：

Java (RxJava)

public class PageKeyedRemoteMediator
  extends RxRemoteMediator<Integer, RedditPost> {

  @NonNull
  private RedditDb db;
  @NonNull
  private RedditPostDao postDao;
  @NonNull
  private SubredditRemoteKeyDao remoteKeyDao;
  @NonNull
  private RedditApi redditApi;
  @NonNull
  private String subredditName;

  public PageKeyedRemoteMediator(
    @NonNull RedditDb db,
    @NonNull RedditApi redditApi,
    @NonNull String subredditName
    ) {
      this.db = db;
      this.postDao = db.posts();
      this.remoteKeyDao = db.remoteKeys();
      this.redditApi = redditApi;
      this.subredditName = subredditName;
      ...
    }
  }

Java (Guava/LiveData)

public class PageKeyedRemoteMediator
  extends ListenableFutureRemoteMediator<Integer, RedditPost> {

  @NonNull
  private RedditDb db;
  @NonNull
  private RedditPostDao postDao;
  @NonNull
  private SubredditRemoteKeyDao remoteKeyDao;
  @NonNull
  private RedditApi redditApi;
  @NonNull
  private String subredditName;
  @NonNull
  private Executor bgExecutor;

  public PageKeyedRemoteMediator(
    @NonNull RedditDb db,
    @NonNull RedditApi redditApi,
    @NonNull String subredditName,
    @NonNull Executor bgExecutor
  ) {
    this.db = db;
    this.postDao = db.posts();
    this.remoteKeyDao = db.remoteKeys();
    this.redditApi = redditApi;
    this.subredditName = subredditName;
    this.bgExecutor = bgExecutor;
    ...
  }
}

您可以提供 Retrofit 接口和搜索字符串，如测试 Paging 实现的 PagingSource 测试部分所示。提供 Room 数据库的模拟版本非常复杂，而更简单的做法是提供数据库的内存中实现，而不是完整的模拟版本。由于创建 Room 数据库需要 Context 对象，您必须将此 RemoteMediator 测试放在 androidTest 目录中，并使用 AndroidJUnit4 测试运行程序来执行此测试，使其能够访问测试应用上下文。如需详细了解插桩测试，请参阅构建插桩单元测试。

定义拆解函数，以确保状态不会在测试函数之间泄漏。这可确保测试运行之间结果的一致。

Java (RxJava)

@RunWith(AndroidJUnit4.class)
public class PageKeyedRemoteMediatorTest {
  static PostFactory postFactory = new PostFactory();
  static List<RedditPost> mockPosts = new ArrayList<>();
  static MockRedditApi mockApi = new MockRedditApi();
  private RedditDb mockDb = RedditDb.Companion.create(
    ApplicationProvider.getApplicationContext(),
    true
  );

  static {
    for (int i=0; i<3; i++) {
      RedditPost post = postFactory.createRedditPost(DEFAULT_SUBREDDIT);
      mockPosts.add(post);
    }
  }

  @After
  public void tearDown() {
    mockDb.clearAllTables();
    // Clear the failure message after each test run.
    mockApi.setFailureMsg(null);
    // Clear out posts after each test run.
    mockApi.clearPosts();
  }
}

Java (Guava/LiveData)

@RunWith(AndroidJUnit4.class)
public class PageKeyedRemoteMediatorTest {
  static PostFactory postFactory = new PostFactory();
  static List<RedditPost> mockPosts = new ArrayList<>();
  static MockRedditApi mockApi = new MockRedditApi();

  private RedditDb mockDb = RedditDb.Companion.create(
    ApplicationProvider.getApplicationContext(),
    true
  );

  static {
    for (int i=0; i<3; i++) {
      RedditPost post = postFactory.createRedditPost(DEFAULT_SUBREDDIT);
      mockPosts.add(post);
    }
  }

  @After
  public void tearDown() {
    mockDb.clearAllTables();
    // Clear the failure message after each test run.
    mockApi.setFailureMsg(null);
    // Clear out posts after each test run.
    mockApi.clearPosts();
  }
}

下一步是测试 load() 函数。在此示例中，要测试三种情况：

第一种情况是 mockApi 返回有效数据。load() 函数应返回 MediatorResult.Success，endOfPaginationReached 属性应为 false。
第二种情况是 mockApi 返回成功响应，但返回的数据为空。load 函数应返回 MediatorResult.Success，endOfPaginationReached 属性应为 true。
第三种情况是 mockApi 在获取数据时抛出异常。load() 函数应返回 MediatorResult.Error。

请按以下步骤测试第一种情况：

使用要返回的 post 数据设置 mockApi。
初始化 RemoteMediator 对象：
测试 load 函数。

Java (RxJava)

@Test
public void refreshLoadReturnsSuccessResultWhenMoreDataIsPresent()
  throws InterruptedException {

  // Add mock results for the API to return.
  for (RedditPost post: mockPosts) {
    mockApi.addPost(post);
  }

  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );
  remoteMediator.loadSingle(LoadType.REFRESH, pagingState)
    .test()
    .await()
    .assertValueCount(1)
    .assertValue(value -> value instanceof RemoteMediator.MediatorResult.Success &&
      ((RemoteMediator.MediatorResult.Success) value).endOfPaginationReached() == false);
}

Java (Guava/LiveData)

@Test
public void refreshLoadReturnsSuccessResultWhenMoreDataIsPresent()
  throws InterruptedException, ExecutionException {

  // Add mock results for the API to return.
  for (RedditPost post: mockPosts) {
    mockApi.addPost(post);
  }

  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT,
    new CurrentThreadExecutor()
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );

  RemoteMediator.MediatorResult result =
    remoteMediator.loadFuture(LoadType.REFRESH, pagingState).get();

  assertThat(result, instanceOf(RemoteMediator.MediatorResult.Success.class));
  assertFalse(((RemoteMediator.MediatorResult.Success) result).endOfPaginationReached());
}

第二个测试要求 mockApi 返回一个空结果。由于您在每次运行测试后都清除 mockApi 中的数据，因此默认情况下它会返回一个空结果。

Java (RxJava)

@Test
public void refreshLoadSuccessAndEndOfPaginationWhenNoMoreData()
  throws InterruptedException() {

  // To test endOfPaginationReached, don't set up the mockApi to return post
  // data here.
  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );
  remoteMediator.loadSingle(LoadType.REFRESH, pagingState)
    .test()
    .await()
    .assertValueCount(1)
    .assertValue(value -> value instanceof RemoteMediator.MediatorResult.Success &&
      ((RemoteMediator.MediatorResult.Success) value).endOfPaginationReached() == true);
}

Java (Guava/LiveData)

@Test
public void refreshLoadSuccessAndEndOfPaginationWhenNoMoreData()
  throws InterruptedException, ExecutionException {

  // To test endOfPaginationReached, don't set up the mockApi to return post
  // data here.
  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT,
    new CurrentThreadExecutor()
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );

  RemoteMediator.MediatorResult result =
    remoteMediator.loadFuture(LoadType.REFRESH, pagingState).get();

  assertThat(result, instanceOf(RemoteMediator.MediatorResult.Success.class));
  assertTrue(((RemoteMediator.MediatorResult.Success) result).endOfPaginationReached());
}

最后一项测试要求 mockApi 抛出异常，以便测试可以验证 load() 函数是否会正确返回 MediatorResult.Error。

Java (RxJava)

@Test
public void refreshLoadReturnsErrorResultWhenErrorOccurs()
  throws InterruptedException {

  // Set up failure message to throw exception from the mock API.
  mockApi.setFailureMsg("Throw test failure");
  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );
  remoteMediator.loadSingle(LoadType.REFRESH, pagingState)
    .test()
    .await()
    .assertValueCount(1)
    .assertValue(value -> value instanceof RemoteMediator.MediatorResult.Error);
}

Java (Guava/LiveData)

@Test
public void refreshLoadReturnsErrorResultWhenErrorOccurs()
  throws InterruptedException, ExecutionException {

  // Set up failure message to throw exception from the mock API.
  mockApi.setFailureMsg("Throw test failure");
  PageKeyedRemoteMediator remoteMediator = new PageKeyedRemoteMediator(
    mockDb,
    mockApi,
    SubRedditViewModel.DEFAULT_SUBREDDIT,
    new CurrentThreadExecutor()
  );
  PagingState<Integer, RedditPost> pagingState = new PagingState<>(
    new ArrayList(),
    null,
    new PagingConfig(10),
    10
  );
  RemoteMediator.MediatorResult result =
    remoteMediator.loadFuture(LoadType.REFRESH, pagingState).get();

  assertThat(result, instanceOf(RemoteMediator.MediatorResult.Error.class));
}

端到端测试

单元测试可确保各个 Paging 组件在单独运行时可以正常工作，而端到端测试则可确保应用作为一个整体运行正常。这些测试仍需要一些模拟依赖项，但通常会涵盖您的大部分应用代码。

本部分中的示例使用模拟 API 依赖项，以避免在测试中使用网络。模拟 API 配置为返回一组一致的测试数据，从而使测试具有可重复性。根据每个依赖项的功能、输出的一致性以及测试所需的准确性，确定要为模拟实现换出哪些依赖项。

编写代码时，应使其能够轻松换入依赖项的模拟版本。以下示例使用基本服务定位器实现来提供和更改依赖项（如果需要）。在较大的应用中，使用Hilt等依赖项注入库有助于管理更复杂的依赖项图。

Kotlin

class RedditActivityTest {

  companion object {
    private const val TEST_SUBREDDIT = "test"
  }

  private val postFactory = PostFactory()
  private val mockApi = MockRedditApi().apply {
    addPost(postFactory.createRedditPost(DEFAULT_SUBREDDIT))
    addPost(postFactory.createRedditPost(TEST_SUBREDDIT))
    addPost(postFactory.createRedditPost(TEST_SUBREDDIT))
  }

  @Before
  fun init() {
    val app = ApplicationProvider.getApplicationContext<Application>()
    // Use a controlled service locator with a mock API.
    ServiceLocator.swap(
      object : DefaultServiceLocator(app = app, useInMemoryDb = true) {
        override fun getRedditApi(): RedditApi = mockApi
      }
    )
  }
}

Java (RxJava)

public class RedditActivityTest {

  public static final String TEST_SUBREDDIT = "test";

  private static PostFactory postFactory = new PostFactory();
  private static MockRedditApi mockApi = new MockRedditApi();

  static {
    mockApi.addPost(postFactory.createRedditPost(DEFAULT_SUBREDDIT));
    mockApi.addPost(postFactory.createRedditPost(TEST_SUBREDDIT));
    mockApi.addPost(postFactory.createRedditPost(TEST_SUBREDDIT));
  }

  @Before
  public void setup() {
    Application app = ApplicationProvider.getApplicationContext();
    // Use a controlled service locator with a mock API.
    ServiceLocator.Companion.swap(
      new DefaultServiceLocator(app, true) {
        @NotNull
        @Override
        public RedditApi getRedditApi() {
          return mockApi;
        }
      }
    );
  }
}

Java (Guava/LiveData)

public class RedditActivityTest {

  public static final String TEST_SUBREDDIT = "test";

  private static PostFactory postFactory = new PostFactory();
  private static MockRedditApi mockApi = new MockRedditApi();

  static {
    mockApi.addPost(postFactory.createRedditPost(DEFAULT_SUBREDDIT));
    mockApi.addPost(postFactory.createRedditPost(TEST_SUBREDDIT));
    mockApi.addPost(postFactory.createRedditPost(TEST_SUBREDDIT));
  }

  @Before
  public void setup() {
    Application app = ApplicationProvider.getApplicationContext();
    // Use a controlled service locator with a mock API.
    ServiceLocator.Companion.swap(
      new DefaultServiceLocator(app, true) {
        @NotNull
        @Override
        public RedditApi getRedditApi() {
          return mockApi;
        }
      }
    );
  }
}

设置测试结构后，下一步是验证 Pager 实现返回的数据是否正确。应有一个测试来确保在页面首次加载时 Pager 对象会加载默认数据，还应有一个测试来验证 Pager 对象是否会根据用户输入正确加载其他数据。

在以下示例中，测试会验证：当用户输入不同的 subreddit 进行搜索时，Pager 对象是否会使用从 API 返回的正确数量的项来更新 RecyclerView.Adapter。

Kotlin

@Test
fun loadsTheDefaultResults() {
    ActivityScenario.launch(RedditActivity::class.java)

    onView(withId(R.id.list)).check { view, noViewFoundException ->
        if (noViewFoundException != null) {
            throw noViewFoundException
        }

        val recyclerView = view as RecyclerView
        assertEquals(1, recyclerView.adapter?.itemCount)
    }
}

@Test
// Verify that the default data is swapped out when the user searches for a
// different subreddit.
fun loadsTheTestResultsWhenSearchingForSubreddit() {
  ActivityScenario.launch(RedditActivity::class.java )

  onView(withId(R.id.list)).check { view, noViewFoundException ->
    if (noViewFoundException != null) {
      throw noViewFoundException
    }

    val recyclerView = view as RecyclerView
    // Verify that it loads the default data first.
    assertEquals(1, recyclerView.adapter?.itemCount)
  }

  // Search for test subreddit instead of default to trigger new data load.
  onView(withId(R.id.input)).perform(
    replaceText(TEST_SUBREDDIT),
    pressKey(KeyEvent.KEYCODE_ENTER)
  )

  onView(withId(R.id.list)).check { view, noViewFoundException ->
    if (noViewFoundException != null) {
      throw noViewFoundException
    }

    val recyclerView = view as RecyclerView
    assertEquals(2, recyclerView.adapter?.itemCount)
  }
}

Java (RxJava)

@Test
public void loadsTheDefaultResults() {
  ActivityScenario.launch(RedditActivity.class);

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    assertEquals(1, recyclerView.getAdapter().getItemCount());
  });
}

@Test
// Verify that the default data is swapped out when the user searches for a
// different subreddit.
public void loadsTheTestResultsWhenSearchingForSubreddit() {
  ActivityScenario.launch(RedditActivity.class);

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    // Verify that it loads the default data first.
    assertEquals(1, recyclerView.getAdapter().getItemCount());
  });

  // Search for test subreddit instead of default to trigger new data load.
  onView(withId(R.id.input)).perform(
    replaceText(TEST_SUBREDDIT),
    pressKey(KeyEvent.KEYCODE_ENTER)
  );

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    assertEquals(2, recyclerView.getAdapter().getItemCount());
  });
}

Java (Guava/LiveData)

@Test
public void loadsTheDefaultResults() {
  ActivityScenario.launch(RedditActivity.class);

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    assertEquals(1, recyclerView.getAdapter().getItemCount());
  });
}

@Test
// Verify that the default data is swapped out when the user searches for a
// different subreddit.
public void loadsTheTestResultsWhenSearchingForSubreddit() {
  ActivityScenario.launch(RedditActivity.class);

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    // Verify that it loads the default data first.
    assertEquals(1, recyclerView.getAdapter().getItemCount());
  });

  // Search for test subreddit instead of default to trigger new data load.
  onView(withId(R.id.input)).perform(
    replaceText(TEST_SUBREDDIT),
    pressKey(KeyEvent.KEYCODE_ENTER)
  );

  onView(withId(R.id.list)).check((view, noViewFoundException) -> {
    if (noViewFoundException != null) {
      throw noViewFoundException;
    }

    RecyclerView recyclerView = (RecyclerView) view;
    assertEquals(2, recyclerView.getAdapter().getItemCount());
  });
}

插桩测试应验证数据是否在界面中正确显示。您可以通过以下两种方式之一来实现此目的：验证 RecyclerView.Adapter 中是否存在正确数量的项，或者遍历各个行视图并验证数据格式是否正确。

测试 Paging 实现 (View) 使用集合让一切井井有条 根据您的偏好保存内容并对其进行分类。

数据层测试

RemoteMediator 测试

Java (RxJava)

Java (Guava/LiveData)

Java (RxJava)

Java (Guava/LiveData)

Java (RxJava)

Java (Guava/LiveData)

Java (RxJava)

Java (Guava/LiveData)

Java (RxJava)

Java (Guava/LiveData)

端到端测试

Kotlin

Java (RxJava)

Java (Guava/LiveData)

Kotlin

Java (RxJava)

Java (Guava/LiveData)

测试 Paging 实现 (View)

`RemoteMediator` 测试