nixos/tests/firefox: add audio subtest

nixos/tests/firefox.nix

@@ -11,26 +11,105 @@ import ./make-test-python.nix ({ pkgs, esr ? false, ... }: {
       environment.systemPackages =
         (if esr then [ pkgs.firefox-esr ] else [ pkgs.firefox ])
         ++ [ pkgs.xdotool ];
+
+      # Need some more memory to record audio.
+      virtualisation.memorySize = "500";
+
+      # Create a virtual sound device, with mixing
+      # and all, for recording audio.
+      boot.kernelModules = [ "snd-aloop" ];
+      sound.enable = true;
+      sound.extraConfig = ''
+        pcm.!default {
+          type plug
+          slave.pcm pcm.dmixer
+        }
+        pcm.dmixer {
+          type dmix
+          ipc_key 1
+          slave {
+            pcm "hw:Loopback,0,0"
+            rate 48000
+            periods 128
+            period_time 0
+            period_size 1024
+            buffer_size 8192
+          }
+        }
+        pcm.recorder {
+          type hw
+          card "Loopback"
+          device 1
+          subdevice 0
+        }
+      '';
+
+      systemd.services.audio-recorder = {
+        description = "Record NixOS test audio to /tmp/record.wav";
+        script = "${pkgs.alsaUtils}/bin/arecord -D recorder -f S16_LE -r48000 /tmp/record.wav";
+      };
+
     };
 
   testScript = ''
+      from contextlib import contextmanager
+
+
+      @contextmanager
+      def audio_recording(machine: Machine) -> None:
+          """
+          Perform actions while recording the
+          machine audio output.
+          """
+          machine.systemctl("start audio-recorder")
+          yield
+          machine.systemctl("stop audio-recorder")
+
+
+      def wait_for_sound(machine: Machine) -> None:
+          """
+          Wait until any sound has been emitted.
+          """
+          machine.wait_for_file("/tmp/record.wav")
+          while True:
+              # Get at most 2M of the recording
+              machine.execute("tail -c 2M /tmp/record.wav > /tmp/last")
+              # Get the exact size
+              size = int(machine.succeed("stat -c '%s' /tmp/last").strip())
+              # Compare it against /dev/zero using `cmp` (skipping 50B of WAVE header).
+              # If some non-NULL bytes are found it returns 1.
+              status, output = machine.execute(
+                  f"cmp -i 50 -n {size - 50} /tmp/last /dev/zero 2>&1"
+              )
+              if status == 1:
+                  break
+              machine.sleep(2)
+
+
       machine.wait_for_x()
 
-      with subtest("wait until Firefox has finished loading the Valgrind docs page"):
+      with subtest("Wait until Firefox has finished loading the Valgrind docs page"):
           machine.execute(
               "xterm -e 'firefox file://${pkgs.valgrind.doc}/share/doc/valgrind/html/index.html' &"
           )
           machine.wait_for_window("Valgrind")
           machine.sleep(40)
 
+      with subtest("Check whether Firefox can play sound"):
+          with audio_recording(machine):
+              machine.succeed(
+                  "firefox file://${pkgs.sound-theme-freedesktop}/share/sounds/freedesktop/stereo/phone-incoming-call.oga &"
+              )
+              wait_for_sound(machine)
+          machine.copy_from_vm("/tmp/record.wav")
+
+      with subtest("Close sound test tab"):
+          machine.execute("xdotool key ctrl+w")
+
       with subtest("Close default browser prompt"):
           machine.execute("xdotool key space")
 
-      with subtest("Hide default browser window"):
-          machine.sleep(2)
-          machine.execute("xdotool key F12")
-
-      with subtest("wait until Firefox draws the developer tool panel"):
+      with subtest("Wait until Firefox draws the developer tool panel"):
           machine.sleep(10)
           machine.succeed("xwininfo -root -tree | grep Valgrind")
           machine.screenshot("screen")