anchor.diff:  
     checkPhase = ''
       runHook preCheck
  +    # newer gettext spews some warnings which fail the tests
  +    substituteInPlace tests/test_po.py --replace "strict=True" "strict=False"
  +    # otherwise tests can't find the app icons; instead of creating index.theme from scratch
  +    # I re-used the one from hicolor-icon-theme which seems to work
  +    cp "${hicolor-icon-theme}/share/icons/hicolor/index.theme" quodlibet/images/hicolor
       env XDG_DATA_DIRS="$out/share:${gtk3}/share/gsettings-schemas/${gtk3.name}:$XDG_ICON_DIRS:$XDG_DATA_DIRS" \
  +      GDK_PIXBUF_MODULE_FILE=${librsvg}/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache \
         HOME=$(mktemp -d) \
         xvfb-run -s '-screen 0 800x600x24' dbus-run-session \
           --config-file=${dbus.daemon}/share/dbus-1/session.conf \
  
positive.code: let optionals = stdenv.lib.optionals; in
  python3.pkgs.buildPythonApplication rec {
    pname = "quodlibet${tag}";
    version = "4.2.1";
  
    src = fetchurl {
      url = "https://github.com/quodlibet/quodlibet/releases/download/release-${version}/quodlibet-${version}.tar.gz";
      sha256 = "0b1rvr4hqs2bjmhayms7vxxkn3d92k9v7p1269rjhf11hpk122l7";
    };
  
    nativeBuildInputs = [ wrapGAppsHook gettext ];
  
    checkInputs = [ gdk-pixbuf ] ++ (with python3.pkgs; [ pytest pytest_xdist polib xvfb_run dbus.daemon glibcLocales ]);
  
    buildInputs = [ gnome3.adwaita-icon-theme libsoup glib glib-networking gtk3 webkitgtk gdk-pixbuf keybinder3 gtksourceview libmodplug libappindicator-gtk3 kakasi gobject-introspection ]
      ++ (if xineBackend then [ xineLib ] else with gst_all_1;
  
negative.code:   pytestFlags = stdenv.lib.optionals (xineBackend || !withGstPlugins) [
      "--ignore=tests/plugin/test_replaygain.py"
    ] ++ [
      # requires networking
      "--ignore=tests/test_browsers_iradio.py"
      # the default theme doesn't have the required icons
      "--ignore=tests/plugin/test_trayicon.py"
      # upstream does actually not enforce source code linting
      "--ignore=tests/quality"
      # build failure on Arch Linux
  