fune/toolkit/content/tests/browser/browser_delay_autoplay_playMediaInMuteTab.js

const PAGE =
  "https://example.com/browser/toolkit/content/tests/browser/file_nonAutoplayAudio.html";

function wait_for_event(browser, event) {
  return BrowserTestUtils.waitForEvent(browser, event, false, event => {
    is(
      event.originalTarget,
      browser,
      "Event must be dispatched to correct browser."
    );
    return true;
  });
}

function check_audio_volume_and_mute(expectedMute) {
  var audio = content.document.getElementById("testAudio");
  if (!audio) {
    ok(false, "Can't get the audio element!");
  }

  let expectedVolume = expectedMute ? 0.0 : 1.0;
  is(expectedVolume, audio.computedVolume, "Audio's volume is correct!");
  is(expectedMute, audio.computedMuted, "Audio's mute state is correct!");
}

function check_audio_pause_state(expectedPauseState) {
  var audio = content.document.getElementById("testAudio");
  if (!audio) {
    ok(false, "Can't get the audio element!");
  }

  is(audio.paused, expectedPauseState, "Audio is paused.");
}

function play_audio() {
  var audio = content.document.getElementById("testAudio");
  if (!audio) {
    ok(false, "Can't get the audio element!");
  }

  audio.play();
  ok(audio.paused, "Can't play audio, because the tab was still blocked.");
}

add_task(async function setup_test_preference() {
  await SpecialPowers.pushPrefEnv({
    set: [
      ["media.useAudioChannelService.testing", true],
      ["media.block-autoplay-until-in-foreground", true],
    ],
  });
});

add_task(async function unblock_icon_should_disapear_after_resume_tab() {
  info("- open new background tab -");
  let tab = BrowserTestUtils.addTab(window.gBrowser, PAGE);
  await BrowserTestUtils.browserLoaded(tab.linkedBrowser);

  info("- audio doesn't be started in beginning -");
  await SpecialPowers.spawn(tab.linkedBrowser, [true], check_audio_pause_state);

  info("- audio shouldn't be muted -");
  await SpecialPowers.spawn(
    tab.linkedBrowser,
    [false],
    check_audio_volume_and_mute
  );

  info("- tab shouldn't display unblocking icon -");
  await waitForTabBlockEvent(tab, false);

  info("- mute tab -");
  tab.linkedBrowser.mute();
  ok(tab.linkedBrowser.audioMuted, "Audio should be muted now");

  info("- try to start audio in background tab -");
  await SpecialPowers.spawn(tab.linkedBrowser, [], play_audio);

  info("- tab should display unblocking icon -");
  await waitForTabBlockEvent(tab, true);

  info("- select tab as foreground tab -");
  await BrowserTestUtils.switchTab(window.gBrowser, tab);

  info("- audio shoule be muted, but not be blocked -");
  await SpecialPowers.spawn(
    tab.linkedBrowser,
    [true],
    check_audio_volume_and_mute
  );

  info("- tab should not display unblocking icon -");
  await waitForTabBlockEvent(tab, false);

  info("- remove tab -");
  BrowserTestUtils.removeTab(tab);
});