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Testing DownloadHelper Track Selection Workflow in SmartTube

This test suite validates the DownloadHelper class functionality in ExoPlayer, focusing on track selection, manifest handling, and download request generation. The tests ensure proper management of media tracks, languages, and download configurations across multiple periods.
Test Coverage Overview

The test suite provides comprehensive coverage of DownloadHelper’s core functionality including:
Manifest and track group retrieval
Track selection management across multiple periods
Audio and text language selection handling
Download request generation with stream key mapping
Edge cases with different track combinations and selections
Implementation Analysis

The testing approach uses a combination of mock objects and fake implementations to isolate DownloadHelper behavior. It leverages Robolectric for Android framework simulation and JUnit for test execution. The tests validate both the public API and internal state management through carefully structured test cases.
Technical Details

Testing Framework: JUnit with AndroidJUnit4 runner
Mocking: Robolectric for Android components
Helper Classes: FakeMediaSource, FakeMediaPeriod for media pipeline simulation
Test Data: Predefined formats and track groups for video, audio and text
Best Practices Demonstrated

The test suite demonstrates several testing best practices:
Thorough setup and teardown management
Comprehensive assertion coverage
Clear test case organization
Effective use of helper methods and utilities
Proper isolation of system under test
yuliskov/smarttube

exoplayer-amzn-2.10.6/library/core/src/test/java/com/google/android/exoplayer2/offline/DownloadHelperTest.java
            
/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.android.exoplayer2.offline;

import static com.google.common.truth.Truth.assertThat;

import android.net.Uri;
import androidx.test.ext.junit.runners.AndroidJUnit4;
import com.google.android.exoplayer2.C;
import com.google.android.exoplayer2.Format;
import com.google.android.exoplayer2.Renderer;
import com.google.android.exoplayer2.RenderersFactory;
import com.google.android.exoplayer2.Timeline;
import com.google.android.exoplayer2.offline.DownloadHelper.Callback;
import com.google.android.exoplayer2.source.MediaPeriod;
import com.google.android.exoplayer2.source.MediaSourceEventListener.EventDispatcher;
import com.google.android.exoplayer2.source.TrackGroup;
import com.google.android.exoplayer2.source.TrackGroupArray;
import com.google.android.exoplayer2.testutil.FakeMediaPeriod;
import com.google.android.exoplayer2.testutil.FakeMediaSource;
import com.google.android.exoplayer2.testutil.FakeRenderer;
import com.google.android.exoplayer2.testutil.FakeTimeline;
import com.google.android.exoplayer2.testutil.FakeTimeline.TimelineWindowDefinition;
import com.google.android.exoplayer2.testutil.RobolectricUtil;
import com.google.android.exoplayer2.trackselection.DefaultTrackSelector;
import com.google.android.exoplayer2.trackselection.DefaultTrackSelector.ParametersBuilder;
import com.google.android.exoplayer2.trackselection.MappingTrackSelector.MappedTrackInfo;
import com.google.android.exoplayer2.trackselection.TrackSelection;
import com.google.android.exoplayer2.upstream.Allocator;
import com.google.android.exoplayer2.util.ConditionVariable;
import com.google.android.exoplayer2.util.MimeTypes;
import com.google.android.exoplayer2.util.Util;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.atomic.AtomicReference;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.annotation.Config;
import org.robolectric.shadows.ShadowLooper;

/** Unit tests for {@link DownloadHelper}. */
@RunWith(AndroidJUnit4.class)
@Config(shadows = {RobolectricUtil.CustomLooper.class, RobolectricUtil.CustomMessageQueue.class})
public class DownloadHelperTest {

  private static final String TEST_DOWNLOAD_TYPE = "downloadType";
  private static final String TEST_CACHE_KEY = "cacheKey";
  private static final Timeline TEST_TIMELINE =
      new FakeTimeline(new TimelineWindowDefinition(/* periodCount= */ 2, /* id= */ new Object()));
  private static final Object TEST_MANIFEST = new Object();

  private static final Format VIDEO_FORMAT_LOW = createVideoFormat(/* bitrate= */ 200_000);
  private static final Format VIDEO_FORMAT_HIGH = createVideoFormat(/* bitrate= */ 800_000);
  private static final Format AUDIO_FORMAT_US = createAudioFormat(/* language= */ "US");
  private static final Format AUDIO_FORMAT_ZH = createAudioFormat(/* language= */ "ZH");
  private static final Format TEXT_FORMAT_US = createTextFormat(/* language= */ "US");
  private static final Format TEXT_FORMAT_ZH = createTextFormat(/* language= */ "ZH");

  private static final TrackGroup TRACK_GROUP_VIDEO_BOTH =
      new TrackGroup(VIDEO_FORMAT_LOW, VIDEO_FORMAT_HIGH);
  private static final TrackGroup TRACK_GROUP_VIDEO_SINGLE = new TrackGroup(VIDEO_FORMAT_LOW);
  private static final TrackGroup TRACK_GROUP_AUDIO_US = new TrackGroup(AUDIO_FORMAT_US);
  private static final TrackGroup TRACK_GROUP_AUDIO_ZH = new TrackGroup(AUDIO_FORMAT_ZH);
  private static final TrackGroup TRACK_GROUP_TEXT_US = new TrackGroup(TEXT_FORMAT_US);
  private static final TrackGroup TRACK_GROUP_TEXT_ZH = new TrackGroup(TEXT_FORMAT_ZH);
  private static final TrackGroupArray TRACK_GROUP_ARRAY_ALL =
      new TrackGroupArray(
          TRACK_GROUP_VIDEO_BOTH,
          TRACK_GROUP_AUDIO_US,
          TRACK_GROUP_AUDIO_ZH,
          TRACK_GROUP_TEXT_US,
          TRACK_GROUP_TEXT_ZH);
  private static final TrackGroupArray TRACK_GROUP_ARRAY_SINGLE =
      new TrackGroupArray(TRACK_GROUP_VIDEO_SINGLE, TRACK_GROUP_AUDIO_US);
  private static final TrackGroupArray[] TRACK_GROUP_ARRAYS =
      new TrackGroupArray[] {TRACK_GROUP_ARRAY_ALL, TRACK_GROUP_ARRAY_SINGLE};

  private Uri testUri;

  private DownloadHelper downloadHelper;

  @Before
  public void setUp() {
    testUri = Uri.parse("http://test.uri");

    FakeRenderer videoRenderer = new FakeRenderer(VIDEO_FORMAT_LOW, VIDEO_FORMAT_HIGH);
    FakeRenderer audioRenderer = new FakeRenderer(AUDIO_FORMAT_US, AUDIO_FORMAT_ZH);
    FakeRenderer textRenderer = new FakeRenderer(TEXT_FORMAT_US, TEXT_FORMAT_ZH);
    RenderersFactory renderersFactory =
        (handler, videoListener, audioListener, metadata, text, drm) ->
            new Renderer[] {textRenderer, audioRenderer, videoRenderer};

    downloadHelper =
        new DownloadHelper(
            TEST_DOWNLOAD_TYPE,
            testUri,
            TEST_CACHE_KEY,
            new TestMediaSource(),
            DownloadHelper.DEFAULT_TRACK_SELECTOR_PARAMETERS,
            Util.getRendererCapabilities(renderersFactory, /* drmSessionManager= */ null));
  }

  @Test
  public void getManifest_returnsManifest() throws Exception {
    prepareDownloadHelper(downloadHelper);

    Object manifest = downloadHelper.getManifest();

    assertThat(manifest).isEqualTo(TEST_MANIFEST);
  }

  @Test
  public void getPeriodCount_returnsPeriodCount() throws Exception {
    prepareDownloadHelper(downloadHelper);

    int periodCount = downloadHelper.getPeriodCount();

    assertThat(periodCount).isEqualTo(2);
  }

  @Test
  public void getTrackGroups_returnsTrackGroups() throws Exception {
    prepareDownloadHelper(downloadHelper);

    TrackGroupArray trackGroupArrayPeriod0 = downloadHelper.getTrackGroups(/* periodIndex= */ 0);
    TrackGroupArray trackGroupArrayPeriod1 = downloadHelper.getTrackGroups(/* periodIndex= */ 1);

    assertThat(trackGroupArrayPeriod0).isEqualTo(TRACK_GROUP_ARRAYS[0]);
    assertThat(trackGroupArrayPeriod1).isEqualTo(TRACK_GROUP_ARRAYS[1]);
  }

  @Test
  public void getMappedTrackInfo_returnsMappedTrackInfo() throws Exception {
    prepareDownloadHelper(downloadHelper);

    MappedTrackInfo mappedTracks0 = downloadHelper.getMappedTrackInfo(/* periodIndex= */ 0);
    MappedTrackInfo mappedTracks1 = downloadHelper.getMappedTrackInfo(/* periodIndex= */ 1);

    assertThat(mappedTracks0.getRendererCount()).isEqualTo(3);
    assertThat(mappedTracks0.getRendererType(/* rendererIndex= */ 0)).isEqualTo(C.TRACK_TYPE_TEXT);
    assertThat(mappedTracks0.getRendererType(/* rendererIndex= */ 1)).isEqualTo(C.TRACK_TYPE_AUDIO);
    assertThat(mappedTracks0.getRendererType(/* rendererIndex= */ 2)).isEqualTo(C.TRACK_TYPE_VIDEO);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 0).length).isEqualTo(2);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 1).length).isEqualTo(2);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 2).length).isEqualTo(1);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 0).get(/* index= */ 0))
        .isEqualTo(TRACK_GROUP_TEXT_US);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 0).get(/* index= */ 1))
        .isEqualTo(TRACK_GROUP_TEXT_ZH);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 1).get(/* index= */ 0))
        .isEqualTo(TRACK_GROUP_AUDIO_US);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 1).get(/* index= */ 1))
        .isEqualTo(TRACK_GROUP_AUDIO_ZH);
    assertThat(mappedTracks0.getTrackGroups(/* rendererIndex= */ 2).get(/* index= */ 0))
        .isEqualTo(TRACK_GROUP_VIDEO_BOTH);

    assertThat(mappedTracks1.getRendererCount()).isEqualTo(3);
    assertThat(mappedTracks1.getRendererType(/* rendererIndex= */ 0)).isEqualTo(C.TRACK_TYPE_TEXT);
    assertThat(mappedTracks1.getRendererType(/* rendererIndex= */ 1)).isEqualTo(C.TRACK_TYPE_AUDIO);
    assertThat(mappedTracks1.getRendererType(/* rendererIndex= */ 2)).isEqualTo(C.TRACK_TYPE_VIDEO);
    assertThat(mappedTracks1.getTrackGroups(/* rendererIndex= */ 0).length).isEqualTo(0);
    assertThat(mappedTracks1.getTrackGroups(/* rendererIndex= */ 1).length).isEqualTo(1);
    assertThat(mappedTracks1.getTrackGroups(/* rendererIndex= */ 2).length).isEqualTo(1);
    assertThat(mappedTracks1.getTrackGroups(/* rendererIndex= */ 1).get(/* index= */ 0))
        .isEqualTo(TRACK_GROUP_AUDIO_US);
    assertThat(mappedTracks1.getTrackGroups(/* rendererIndex= */ 2).get(/* index= */ 0))
        .isEqualTo(TRACK_GROUP_VIDEO_SINGLE);
  }

  @Test
  public void getTrackSelections_returnsInitialSelection() throws Exception {
    prepareDownloadHelper(downloadHelper);

    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertSingleTrackSelectionEquals(selectedText0, TRACK_GROUP_TEXT_US, 0);
    assertSingleTrackSelectionEquals(selectedAudio0, TRACK_GROUP_AUDIO_US, 0);
    assertSingleTrackSelectionEquals(selectedVideo0, TRACK_GROUP_VIDEO_BOTH, 1);

    assertThat(selectedText1).isEmpty();
    assertSingleTrackSelectionEquals(selectedAudio1, TRACK_GROUP_AUDIO_US, 0);
    assertSingleTrackSelectionEquals(selectedVideo1, TRACK_GROUP_VIDEO_SINGLE, 0);
  }

  @Test
  public void getTrackSelections_afterClearTrackSelections_isEmpty() throws Exception {
    prepareDownloadHelper(downloadHelper);

    // Clear only one period selection to verify second period selection is untouched.
    downloadHelper.clearTrackSelections(/* periodIndex= */ 0);
    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertThat(selectedText0).isEmpty();
    assertThat(selectedAudio0).isEmpty();
    assertThat(selectedVideo0).isEmpty();

    // Verify
    assertThat(selectedText1).isEmpty();
    assertSingleTrackSelectionEquals(selectedAudio1, TRACK_GROUP_AUDIO_US, 0);
    assertSingleTrackSelectionEquals(selectedVideo1, TRACK_GROUP_VIDEO_SINGLE, 0);
  }

  @Test
  public void getTrackSelections_afterReplaceTrackSelections_returnsNewSelections()
      throws Exception {
    prepareDownloadHelper(downloadHelper);
    DefaultTrackSelector.Parameters parameters =
        new ParametersBuilder()
            .setPreferredAudioLanguage("ZH")
            .setPreferredTextLanguage("ZH")
            .setRendererDisabled(/* rendererIndex= */ 2, true)
            .build();

    // Replace only one period selection to verify second period selection is untouched.
    downloadHelper.replaceTrackSelections(/* periodIndex= */ 0, parameters);
    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertSingleTrackSelectionEquals(selectedText0, TRACK_GROUP_TEXT_ZH, 0);
    assertSingleTrackSelectionEquals(selectedAudio0, TRACK_GROUP_AUDIO_ZH, 0);
    assertThat(selectedVideo0).isEmpty();

    assertThat(selectedText1).isEmpty();
    assertSingleTrackSelectionEquals(selectedAudio1, TRACK_GROUP_AUDIO_US, 0);
    assertSingleTrackSelectionEquals(selectedVideo1, TRACK_GROUP_VIDEO_SINGLE, 0);
  }

  @Test
  public void getTrackSelections_afterAddTrackSelections_returnsCombinedSelections()
      throws Exception {
    prepareDownloadHelper(downloadHelper);
    // Select parameters to require some merging of track groups because the new parameters add
    // all video tracks to initial video single track selection.
    DefaultTrackSelector.Parameters parameters =
        new ParametersBuilder()
            .setPreferredAudioLanguage("ZH")
            .setPreferredTextLanguage("US")
            .build();

    // Add only to one period selection to verify second period selection is untouched.
    downloadHelper.addTrackSelection(/* periodIndex= */ 0, parameters);
    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertSingleTrackSelectionEquals(selectedText0, TRACK_GROUP_TEXT_US, 0);
    assertThat(selectedAudio0).hasSize(2);
    assertTrackSelectionEquals(selectedAudio0.get(0), TRACK_GROUP_AUDIO_US, 0);
    assertTrackSelectionEquals(selectedAudio0.get(1), TRACK_GROUP_AUDIO_ZH, 0);
    assertSingleTrackSelectionEquals(selectedVideo0, TRACK_GROUP_VIDEO_BOTH, 0, 1);

    assertThat(selectedText1).isEmpty();
    assertSingleTrackSelectionEquals(selectedAudio1, TRACK_GROUP_AUDIO_US, 0);
    assertSingleTrackSelectionEquals(selectedVideo1, TRACK_GROUP_VIDEO_SINGLE, 0);
  }

  @Test
  public void getTrackSelections_afterAddAudioLanguagesToSelection_returnsCombinedSelections()
      throws Exception {
    prepareDownloadHelper(downloadHelper);
    downloadHelper.clearTrackSelections(/* periodIndex= */ 0);
    downloadHelper.clearTrackSelections(/* periodIndex= */ 1);

    // Add a non-default language, and a non-existing language (which will select the default).
    downloadHelper.addAudioLanguagesToSelection("ZH", "Klingonese");
    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertThat(selectedVideo0).isEmpty();
    assertThat(selectedText0).isEmpty();
    assertThat(selectedAudio0).hasSize(2);
    assertTrackSelectionEquals(selectedAudio0.get(0), TRACK_GROUP_AUDIO_ZH, 0);
    assertTrackSelectionEquals(selectedAudio0.get(1), TRACK_GROUP_AUDIO_US, 0);

    assertThat(selectedVideo1).isEmpty();
    assertThat(selectedText1).isEmpty();
    assertSingleTrackSelectionEquals(selectedAudio1, TRACK_GROUP_AUDIO_US, 0);
  }

  @Test
  public void getTrackSelections_afterAddTextLanguagesToSelection_returnsCombinedSelections()
      throws Exception {
    prepareDownloadHelper(downloadHelper);
    downloadHelper.clearTrackSelections(/* periodIndex= */ 0);
    downloadHelper.clearTrackSelections(/* periodIndex= */ 1);

    // Add a non-default language, and a non-existing language (which will select the default).
    downloadHelper.addTextLanguagesToSelection(
        /* selectUndeterminedTextLanguage= */ true, "ZH", "Klingonese");
    List<TrackSelection> selectedText0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo0 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 0, /* rendererIndex= */ 2);
    List<TrackSelection> selectedText1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 0);
    List<TrackSelection> selectedAudio1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 1);
    List<TrackSelection> selectedVideo1 =
        downloadHelper.getTrackSelections(/* periodIndex= */ 1, /* rendererIndex= */ 2);

    assertThat(selectedVideo0).isEmpty();
    assertThat(selectedAudio0).isEmpty();
    assertThat(selectedText0).hasSize(2);
    assertTrackSelectionEquals(selectedText0.get(0), TRACK_GROUP_TEXT_ZH, 0);
    assertTrackSelectionEquals(selectedText0.get(1), TRACK_GROUP_TEXT_US, 0);

    assertThat(selectedVideo1).isEmpty();
    assertThat(selectedAudio1).isEmpty();
    assertThat(selectedText1).isEmpty();
  }

  @Test
  public void getDownloadRequest_createsDownloadRequest_withAllSelectedTracks() throws Exception {
    prepareDownloadHelper(downloadHelper);
    // Ensure we have track groups with multiple indices, renderers with multiple track groups and
    // also renderers without any track groups.
    DefaultTrackSelector.Parameters parameters =
        new ParametersBuilder()
            .setPreferredAudioLanguage("ZH")
            .setPreferredTextLanguage("US")
            .build();
    downloadHelper.addTrackSelection(/* periodIndex= */ 0, parameters);
    byte[] data = new byte[10];
    Arrays.fill(data, (byte) 123);

    DownloadRequest downloadRequest = downloadHelper.getDownloadRequest(data);

    assertThat(downloadRequest.type).isEqualTo(TEST_DOWNLOAD_TYPE);
    assertThat(downloadRequest.uri).isEqualTo(testUri);
    assertThat(downloadRequest.customCacheKey).isEqualTo(TEST_CACHE_KEY);
    assertThat(downloadRequest.data).isEqualTo(data);
    assertThat(downloadRequest.streamKeys)
        .containsExactly(
            new StreamKey(/* periodIndex= */ 0, /* groupIndex= */ 0, /* trackIndex= */ 0),
            new StreamKey(/* periodIndex= */ 0, /* groupIndex= */ 0, /* trackIndex= */ 1),
            new StreamKey(/* periodIndex= */ 0, /* groupIndex= */ 1, /* trackIndex= */ 0),
            new StreamKey(/* periodIndex= */ 0, /* groupIndex= */ 2, /* trackIndex= */ 0),
            new StreamKey(/* periodIndex= */ 0, /* groupIndex= */ 3, /* trackIndex= */ 0),
            new StreamKey(/* periodIndex= */ 1, /* groupIndex= */ 0, /* trackIndex= */ 0),
            new StreamKey(/* periodIndex= */ 1, /* groupIndex= */ 1, /* trackIndex= */ 0));
  }

  private static void prepareDownloadHelper(DownloadHelper downloadHelper) throws Exception {
    AtomicReference<Exception> prepareException = new AtomicReference<>(null);
    ConditionVariable preparedCondition = new ConditionVariable();
    downloadHelper.prepare(
        new Callback() {
          @Override
          public void onPrepared(DownloadHelper helper) {
            preparedCondition.open();
          }

          @Override
          public void onPrepareError(DownloadHelper helper, IOException e) {
            prepareException.set(e);
            preparedCondition.open();
          }
        });
    while (!preparedCondition.block(0)) {
      ShadowLooper.runMainLooperToNextTask();
    }
    if (prepareException.get() != null) {
      throw prepareException.get();
    }
  }

  private static Format createVideoFormat(int bitrate) {
    return Format.createVideoSampleFormat(
        /* id= */ null,
        /* sampleMimeType= */ MimeTypes.VIDEO_H264,
        /* codecs= */ null,
        /* bitrate= */ bitrate,
        /* maxInputSize= */ Format.NO_VALUE,
        /* width= */ 480,
        /* height= */ 360,
        /* frameRate= */ Format.NO_VALUE,
        /* initializationData= */ null,
        /* drmInitData= */ null);
  }

  private static Format createAudioFormat(String language) {
    return Format.createAudioSampleFormat(
        /* id= */ null,
        /* sampleMimeType= */ MimeTypes.AUDIO_AAC,
        /* codecs= */ null,
        /* bitrate= */ 48000,
        /* maxInputSize= */ Format.NO_VALUE,
        /* channelCount= */ 2,
        /* sampleRate */ 44100,
        /* initializationData= */ null,
        /* drmInitData= */ null,
        /* selectionFlags= */ C.SELECTION_FLAG_DEFAULT,
        /* language= */ language);
  }

  private static Format createTextFormat(String language) {
    return Format.createTextSampleFormat(
        /* id= */ null,
        /* sampleMimeType= */ MimeTypes.TEXT_VTT,
        /* selectionFlags= */ C.SELECTION_FLAG_DEFAULT,
        /* language= */ language);
  }

  private static void assertSingleTrackSelectionEquals(
      List<TrackSelection> trackSelectionList, TrackGroup trackGroup, int... tracks) {
    assertThat(trackSelectionList).hasSize(1);
    assertTrackSelectionEquals(trackSelectionList.get(0), trackGroup, tracks);
  }

  private static void assertTrackSelectionEquals(
      TrackSelection trackSelection, TrackGroup trackGroup, int... tracks) {
    assertThat(trackSelection.getTrackGroup()).isEqualTo(trackGroup);
    assertThat(trackSelection.length()).isEqualTo(tracks.length);
    int[] selectedTracksInGroup = new int[trackSelection.length()];
    for (int i = 0; i < trackSelection.length(); i++) {
      selectedTracksInGroup[i] = trackSelection.getIndexInTrackGroup(i);
    }
    Arrays.sort(selectedTracksInGroup);
    Arrays.sort(tracks);
    assertThat(selectedTracksInGroup).isEqualTo(tracks);
  }

  private static final class TestMediaSource extends FakeMediaSource {

    public TestMediaSource() {
      super(TEST_TIMELINE, TEST_MANIFEST);
    }

    @Override
    public MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator, long startPositionUs) {
      int periodIndex = TEST_TIMELINE.getIndexOfPeriod(id.periodUid);
      return new FakeMediaPeriod(
          TRACK_GROUP_ARRAYS[periodIndex],
          new EventDispatcher()
              .withParameters(/* windowIndex= */ 0, id, /* mediaTimeOffsetMs= */ 0)) {
        @Override
        public List<StreamKey> getStreamKeys(List<TrackSelection> trackSelections) {
          List<StreamKey> result = new ArrayList<>();
          for (TrackSelection trackSelection : trackSelections) {
            int groupIndex =
                TRACK_GROUP_ARRAYS[periodIndex].indexOf(trackSelection.getTrackGroup());
            for (int i = 0; i < trackSelection.length(); i++) {
              result.add(
                  new StreamKey(periodIndex, groupIndex, trackSelection.getIndexInTrackGroup(i)));
            }
          }
          return result;
        }
      };
    }

    @Override
    public void releasePeriod(MediaPeriod mediaPeriod) {
      // Do nothing.
    }
  }
}