quodlibet: improve formatting and add comments

pkgs/applications/audio/quodlibet/default.nix

@@ -33,13 +33,23 @@ python3.pkgs.buildPythonApplication rec {
 
   LC_ALL = "en_US.UTF-8";
 
+  pytestFlags = stdenv.lib.optionals (xineBackend || !withGstPlugins) [
+    "--ignore=tests/plugin/test_replaygain.py"
+  ] ++ [
+    # upstream does actually not enforce source code linting
+    "--ignore=tests/quality"
+    # build failure on Arch Linux
+    # https://github.com/NixOS/nixpkgs/pull/77796#issuecomment-575841355
+    "--ignore=tests/test_operon.py"
+  ];
+
   checkPhase = ''
     runHook preCheck
     env XDG_DATA_DIRS="$out/share:${gtk3}/share/gsettings-schemas/${gtk3.name}:$XDG_ICON_DIRS:$XDG_DATA_DIRS" \
       HOME=$(mktemp -d) \
       xvfb-run -s '-screen 0 800x600x24' dbus-run-session \
         --config-file=${dbus.daemon}/share/dbus-1/session.conf \
-        py.test ${stdenv.lib.optionalString (xineBackend || !withGstPlugins) " --ignore=tests/plugin/test_replaygain.py"} --ignore=tests/quality --ignore=tests/test_operon.py
+        py.test $pytestFlags
     runHook postCheck
   '';