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Testing WebVTT Subtitle Decoder Implementation in SmartTube

This test suite validates the WebvttDecoder implementation in ExoPlayer, focusing on WebVTT subtitle parsing and formatting. It ensures proper handling of various WebVTT subtitle formats, styling options, and positioning parameters.
Test Coverage Overview

The test suite provides comprehensive coverage of WebVTT subtitle decoding functionality, including:
Basic subtitle parsing and timing validation
CSS styling and formatting options
Complex positioning and alignment parameters
Error handling for malformed inputs
Support for BOM markers and special characters
Implementation Analysis

The testing approach uses JUnit and AndroidJUnit4 frameworks to validate WebVTT subtitle processing. Tests systematically verify subtitle timing, text content, styling spans, and positioning attributes through detailed assertions and edge case validation.

The implementation leverages TestUtil for test asset loading and specialized assertion methods for cue verification.
Technical Details

Key technical components include:
JUnit and AndroidJUnit4 test runners
Custom test utilities for byte array handling
Android text styling spans validation
WebVTT test files with various formatting scenarios
Specialized cue assertion helpers
Best Practices Demonstrated

The test suite exemplifies strong testing practices through:
Comprehensive edge case coverage
Detailed assertion messages
Modular test methods
Clear test data organization
Robust validation helpers
yuliskov/smarttube

exoplayer-amzn-2.10.6/library/core/src/test/java/com/google/android/exoplayer2/text/webvtt/WebvttDecoderTest.java
            
/*
 * Copyright (C) 2016 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.text.webvtt;

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.fail;

import android.graphics.Typeface;
import android.text.Layout.Alignment;
import android.text.Spanned;
import android.text.style.BackgroundColorSpan;
import android.text.style.ForegroundColorSpan;
import android.text.style.StyleSpan;
import android.text.style.TypefaceSpan;
import android.text.style.UnderlineSpan;
import androidx.test.core.app.ApplicationProvider;
import androidx.test.ext.junit.runners.AndroidJUnit4;
import com.google.android.exoplayer2.testutil.TestUtil;
import com.google.android.exoplayer2.text.Cue;
import com.google.android.exoplayer2.text.SubtitleDecoderException;
import java.io.IOException;
import java.util.List;
import org.junit.Test;
import org.junit.runner.RunWith;

/** Unit test for {@link WebvttDecoder}. */
@RunWith(AndroidJUnit4.class)
public class WebvttDecoderTest {

  private static final String TYPICAL_FILE = "webvtt/typical";
  private static final String TYPICAL_WITH_BAD_TIMESTAMPS = "webvtt/typical_with_bad_timestamps";
  private static final String TYPICAL_WITH_IDS_FILE = "webvtt/typical_with_identifiers";
  private static final String TYPICAL_WITH_COMMENTS_FILE = "webvtt/typical_with_comments";
  private static final String WITH_POSITIONING_FILE = "webvtt/with_positioning";
  private static final String WITH_BAD_CUE_HEADER_FILE = "webvtt/with_bad_cue_header";
  private static final String WITH_TAGS_FILE = "webvtt/with_tags";
  private static final String WITH_CSS_STYLES = "webvtt/with_css_styles";
  private static final String WITH_CSS_COMPLEX_SELECTORS = "webvtt/with_css_complex_selectors";
  private static final String WITH_BOM = "webvtt/with_bom";
  private static final String EMPTY_FILE = "webvtt/empty";

  @Test
  public void testDecodeEmpty() throws IOException {
    WebvttDecoder decoder = new WebvttDecoder();
    byte[] bytes = TestUtil.getByteArray(ApplicationProvider.getApplicationContext(), EMPTY_FILE);
    try {
      decoder.decode(bytes, bytes.length, /* reset= */ false);
      fail();
    } catch (SubtitleDecoderException expected) {
      // Do nothing.
    }
  }

  @Test
  public void testDecodeTypical() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_FILE);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
  }

  @Test
  public void testDecodeWithBom() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_BOM);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
  }

  @Test
  public void testDecodeTypicalWithBadTimestamps() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_WITH_BAD_TIMESTAMPS);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
  }

  @Test
  public void testDecodeTypicalWithIds() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_WITH_IDS_FILE);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
  }

  @Test
  public void testDecodeTypicalWithComments() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(TYPICAL_WITH_COMMENTS_FILE);

    // test event count
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // test cues
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
  }

  @Test
  public void testDecodeWithTags() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_TAGS_FILE);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(8);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 4,
        /* startTimeUs= */ 4000000,
        /* endTimeUs= */ 5000000,
        "This is the third subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 6,
        /* startTimeUs= */ 6000000,
        /* endTimeUs= */ 7000000,
        "This is the <fourth> &subtitle.");
  }

  @Test
  public void testDecodeWithPositioning() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_POSITIONING_FILE);
    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(12);
    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.",
        Alignment.ALIGN_NORMAL,
        /* line= */ Cue.DIMEN_UNSET,
        /* lineType= */ Cue.TYPE_UNSET,
        /* lineAnchor= */ Cue.TYPE_UNSET,
        /* position= */ 0.1f,
        /* positionAnchor= */ Cue.ANCHOR_TYPE_START,
        /* size= */ 0.35f);
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.",
        Alignment.ALIGN_OPPOSITE,
        /* line= */ Cue.DIMEN_UNSET,
        /* lineType= */ Cue.TYPE_UNSET,
        /* lineAnchor= */ Cue.TYPE_UNSET,
        /* position= */ Cue.DIMEN_UNSET,
        /* positionAnchor= */ Cue.TYPE_UNSET,
        /* size= */ 0.35f);
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 4,
        /* startTimeUs= */ 4000000,
        /* endTimeUs= */ 5000000,
        "This is the third subtitle.",
        Alignment.ALIGN_CENTER,
        /* line= */ 0.45f,
        /* lineType= */ Cue.LINE_TYPE_FRACTION,
        /* lineAnchor= */ Cue.ANCHOR_TYPE_END,
        /* position= */ Cue.DIMEN_UNSET,
        /* positionAnchor= */ Cue.TYPE_UNSET,
        /* size= */ 0.35f);
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 6,
        /* startTimeUs= */ 6000000,
        /* endTimeUs= */ 7000000,
        "This is the fourth subtitle.",
        Alignment.ALIGN_CENTER,
        /* line= */ -11f,
        /* lineType= */ Cue.LINE_TYPE_NUMBER,
        /* lineAnchor= */ Cue.TYPE_UNSET,
        /* position= */ Cue.DIMEN_UNSET,
        /* positionAnchor= */ Cue.TYPE_UNSET,
        /* size= */ Cue.DIMEN_UNSET);
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 8,
        /* startTimeUs= */ 7000000,
        /* endTimeUs= */ 8000000,
        "This is the fifth subtitle.",
        Alignment.ALIGN_OPPOSITE,
        /* line= */ Cue.DIMEN_UNSET,
        /* lineType= */ Cue.TYPE_UNSET,
        /* lineAnchor= */ Cue.TYPE_UNSET,
        /* position= */ 0.1f,
        /* positionAnchor= */ Cue.ANCHOR_TYPE_END,
        /* size= */ 0.1f);
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 10,
        /* startTimeUs= */ 10000000,
        /* endTimeUs= */ 11000000,
        "This is the sixth subtitle.",
        Alignment.ALIGN_CENTER,
        /* line= */ 0.45f,
        /* lineType= */ Cue.LINE_TYPE_FRACTION,
        /* lineAnchor= */ Cue.ANCHOR_TYPE_END,
        /* position= */ Cue.DIMEN_UNSET,
        /* positionAnchor= */ Cue.TYPE_UNSET,
        /* size= */ 0.35f);
  }

  @Test
  public void testDecodeWithBadCueHeader() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_BAD_CUE_HEADER_FILE);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 4000000,
        /* endTimeUs= */ 5000000,
        "This is the third subtitle.");
  }

  @Test
  public void testWebvttWithCssStyle() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_CSS_STYLES);

    // Test event count.
    assertThat(subtitle.getEventTimeCount()).isEqualTo(8);

    // Test cues.
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 0,
        /* startTimeUs= */ 0,
        /* endTimeUs= */ 1234000,
        "This is the first subtitle.");
    assertCue(
        subtitle,
        /* eventTimeIndex= */ 2,
        /* startTimeUs= */ 2345000,
        /* endTimeUs= */ 3456000,
        "This is the second subtitle.");

    Spanned s1 = getUniqueSpanTextAt(subtitle, /* timeUs= */ 0);
    Spanned s2 = getUniqueSpanTextAt(subtitle, /* timeUs= */ 2345000);
    Spanned s3 = getUniqueSpanTextAt(subtitle, /* timeUs= */ 20000000);
    Spanned s4 = getUniqueSpanTextAt(subtitle, /* timeUs= */ 25000000);
    assertThat(s1.getSpans(/* start= */ 0, s1.length(), ForegroundColorSpan.class)).hasLength(1);
    assertThat(s1.getSpans(/* start= */ 0, s1.length(), BackgroundColorSpan.class)).hasLength(1);
    assertThat(s2.getSpans(/* start= */ 0, s2.length(), ForegroundColorSpan.class)).hasLength(2);
    assertThat(s3.getSpans(/* start= */ 10, s3.length(), UnderlineSpan.class)).hasLength(1);
    assertThat(s4.getSpans(/* start= */ 0, /* end= */ 16, BackgroundColorSpan.class)).hasLength(2);
    assertThat(s4.getSpans(/* start= */ 17, s4.length(), StyleSpan.class)).hasLength(1);
    assertThat(s4.getSpans(/* start= */ 17, s4.length(), StyleSpan.class)[0].getStyle())
        .isEqualTo(Typeface.BOLD);
  }

  @Test
  public void testWithComplexCssSelectors() throws IOException, SubtitleDecoderException {
    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_CSS_COMPLEX_SELECTORS);
    Spanned text = getUniqueSpanTextAt(subtitle, /* timeUs= */ 0);
    assertThat(text.getSpans(/* start= */ 30, text.length(), ForegroundColorSpan.class))
        .hasLength(1);
    assertThat(
            text.getSpans(/* start= */ 30, text.length(), ForegroundColorSpan.class)[0]
                .getForegroundColor())
        .isEqualTo(0xFFEE82EE);
    assertThat(text.getSpans(/* start= */ 30, text.length(), TypefaceSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 30, text.length(), TypefaceSpan.class)[0].getFamily())
        .isEqualTo("courier");

    text = getUniqueSpanTextAt(subtitle, /* timeUs= */ 2000000);
    assertThat(text.getSpans(/* start= */ 5, text.length(), TypefaceSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 5, text.length(), TypefaceSpan.class)[0].getFamily())
        .isEqualTo("courier");

    text = getUniqueSpanTextAt(subtitle, /* timeUs= */ 2500000);
    assertThat(text.getSpans(/* start= */ 5, text.length(), StyleSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 5, text.length(), StyleSpan.class)[0].getStyle())
        .isEqualTo(Typeface.BOLD);
    assertThat(text.getSpans(/* start= */ 5, text.length(), TypefaceSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 5, text.length(), TypefaceSpan.class)[0].getFamily())
        .isEqualTo("courier");

    text = getUniqueSpanTextAt(subtitle, /* timeUs= */ 4000000);
    assertThat(text.getSpans(/* start= */ 6, /* end= */ 22, StyleSpan.class)).hasLength(0);
    assertThat(text.getSpans(/* start= */ 30, text.length(), StyleSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 30, text.length(), StyleSpan.class)[0].getStyle())
        .isEqualTo(Typeface.BOLD);

    text = getUniqueSpanTextAt(subtitle, /* timeUs= */ 5000000);
    assertThat(text.getSpans(/* start= */ 9, /* end= */ 17, StyleSpan.class)).hasLength(0);
    assertThat(text.getSpans(/* start= */ 19, text.length(), StyleSpan.class)).hasLength(1);
    assertThat(text.getSpans(/* start= */ 19, text.length(), StyleSpan.class)[0].getStyle())
        .isEqualTo(Typeface.ITALIC);
  }

  private WebvttSubtitle getSubtitleForTestAsset(String asset)
      throws IOException, SubtitleDecoderException {
    WebvttDecoder decoder = new WebvttDecoder();
    byte[] bytes = TestUtil.getByteArray(ApplicationProvider.getApplicationContext(), asset);
    return decoder.decode(bytes, bytes.length, /* reset= */ false);
  }

  private Spanned getUniqueSpanTextAt(WebvttSubtitle sub, long timeUs) {
    return (Spanned) sub.getCues(timeUs).get(0).text;
  }

  private static void assertCue(
      WebvttSubtitle subtitle, int eventTimeIndex, long startTimeUs, int endTimeUs, String text) {
    assertCue(
        subtitle,
        eventTimeIndex,
        startTimeUs,
        endTimeUs,
        text,
        /* textAlignment= */ null,
        /* line= */ Cue.DIMEN_UNSET,
        /* lineType= */ Cue.TYPE_UNSET,
        /* lineAnchor= */ Cue.TYPE_UNSET,
        /* position= */ Cue.DIMEN_UNSET,
        /* positionAnchor= */ Cue.TYPE_UNSET,
        /* size= */ Cue.DIMEN_UNSET);
  }

  private static void assertCue(
      WebvttSubtitle subtitle,
      int eventTimeIndex,
      long startTimeUs,
      int endTimeUs,
      String text,
      Alignment textAlignment,
      float line,
      int lineType,
      int lineAnchor,
      float position,
      int positionAnchor,
      float size) {
    assertThat(subtitle.getEventTime(eventTimeIndex)).isEqualTo(startTimeUs);
    assertThat(subtitle.getEventTime(eventTimeIndex + 1)).isEqualTo(endTimeUs);
    List<Cue> cues = subtitle.getCues(subtitle.getEventTime(eventTimeIndex));
    assertThat(cues).hasSize(1);
    // Assert cue properties.
    Cue cue = cues.get(0);
    assertThat(cue.text.toString()).isEqualTo(text);
    assertThat(cue.textAlignment).isEqualTo(textAlignment);
    assertThat(cue.line).isEqualTo(line);
    assertThat(cue.lineType).isEqualTo(lineType);
    assertThat(cue.lineAnchor).isEqualTo(lineAnchor);
    assertThat(cue.position).isEqualTo(position);
    assertThat(cue.positionAnchor).isEqualTo(positionAnchor);
    assertThat(cue.size).isEqualTo(size);
  }
}