audio: run TestPlayOnIdleContext on the fake clock of synctest

The test was added after the survey in #3716, and waits on real time in
the same way.

Updates #3716

audio/audio_test.go

@@ -879,52 +879,54 @@ func TestPlayerErrorDoesNotStopOtherPlayers(t *testing.T) {
 }
 
 func TestPlayOnIdleContext(t *testing.T) {
-	setup()
-	defer teardown()
+	synctest.Test(t, func(t *testing.T) {
+		setup()
+		defer teardown()
 
-	// The first update creates the audio device, so that the players below play for real.
-	if err := audio.UpdateForTesting(); err != nil {
-		t.Fatal(err)
-	}
-
-	// waitUntil polls cond until it holds or the deadline passes, and reports whether it held.
-	// The deadline is generous because time.Sleep has a several-millisecond floor on browsers.
-	waitUntil := func(cond func() bool) bool {
-		deadline := time.Now().Add(10 * time.Second)
-		for time.Now().Before(deadline) {
-			if cond() {
-				return true
-			}
-			time.Sleep(5 * time.Millisecond)
-		}
-		return false
-	}
-
-	// A player's position is advanced only by the context, so a growing position shows that the
-	// context updates the player. The second round starts a player after the context has dropped
-	// the finished player of the first round, that is, after it went idle by itself.
-	for i := range 2 {
-		// Let the context settle into idling with no player to update.
-		time.Sleep(50 * time.Millisecond)
-
-		// 44100 [Hz] * 4 [bytes/sample] is one second of 16bit stereo audio.
-		p, err := context.NewPlayer(bytes.NewReader(make([]byte, 44100*4)))
-		if err != nil {
+		// The first update creates the audio device, so that the players below play for real.
+		if err := audio.UpdateForTesting(); err != nil {
 			t.Fatal(err)
 		}
-		p.Play()
 
-		if !waitUntil(func() bool { return p.Position() > 0 }) {
-			t.Errorf("round %d: Position() did not advance after Play on an idle context", i)
-			return
+		// waitUntil polls cond until it holds or the deadline passes, and reports whether it held.
+		// The test runs on the fake clock of synctest, so the deadline does not take real time.
+		waitUntil := func(cond func() bool) bool {
+			deadline := time.Now().Add(10 * time.Second)
+			for time.Now().Before(deadline) {
+				if cond() {
+					return true
+				}
+				time.Sleep(5 * time.Millisecond)
+			}
+			return false
 		}
 
-		// The next round needs the context to be idle again, which is only possible once the
-		// context has dropped the finished player.
-		if !waitUntil(func() bool { return audio.PlayersCountForTesting() == 0 }) {
-			t.Fatalf("round %d: time out: the player did not finish", i)
+		// A player's position is advanced only by the context, so a growing position shows that the
+		// context updates the player. The second round starts a player after the context has dropped
+		// the finished player of the first round, that is, after it went idle by itself.
+		for i := range 2 {
+			// Let the context settle into idling with no player to update.
+			time.Sleep(50 * time.Millisecond)
+
+			// 44100 [Hz] * 4 [bytes/sample] is one second of 16bit stereo audio.
+			p, err := context.NewPlayer(bytes.NewReader(make([]byte, 44100*4)))
+			if err != nil {
+				t.Fatal(err)
+			}
+			p.Play()
+
+			if !waitUntil(func() bool { return p.Position() > 0 }) {
+				t.Errorf("round %d: Position() did not advance after Play on an idle context", i)
+				return
+			}
+
+			// The next round needs the context to be idle again, which is only possible once the
+			// context has dropped the finished player.
+			if !waitUntil(func() bool { return audio.PlayersCountForTesting() == 0 }) {
+				t.Fatalf("round %d: time out: the player did not finish", i)
+			}
 		}
-	}
+	})
 }
 
 func callWithTimeout(t *testing.T, name string, f func() error) error {