gnome3.gnome_keyring: clarify Python version & enable tests

pkgs/desktops/gnome-3/core/gnome-keyring/default.nix

@@ -1,6 +1,6 @@
-{ stdenv, fetchurl, pkgconfig, dbus, libgcrypt, libtasn1, pam, python, glib, libxslt
+{ stdenv, fetchurl, pkgconfig, dbus, libgcrypt, libtasn1, pam, python2, glib, libxslt
 , intltool, pango, gcr, gdk_pixbuf, atk, p11_kit, wrapGAppsHook
-, docbook_xsl_ns, docbook_xsl, gnome3 }:
+, docbook_xsl, docbook_xml_dtd_42, gnome3 }:
 
 stdenv.mkDerivation rec {
   inherit (import ./src.nix fetchurl) name src;
@@ -8,21 +8,41 @@ stdenv.mkDerivation rec {
   outputs = [ "out" "dev" ];
 
   buildInputs = with gnome3; [
-    dbus libgcrypt pam python gtk3 gconf libgnome_keyring
+    dbus libgcrypt pam gtk3 gconf libgnome_keyring
     pango gcr gdk_pixbuf atk p11_kit
   ];
 
+  # In 3.20.1, tests do not support Python 3
+  checkInputs = [ dbus python2 ];
+
   propagatedBuildInputs = [ glib libtasn1 libxslt ];
 
-  nativeBuildInputs = [ pkgconfig intltool docbook_xsl_ns docbook_xsl wrapGAppsHook ];
+  nativeBuildInputs = [
+    pkgconfig intltool docbook_xsl docbook_xml_dtd_42 wrapGAppsHook
+  ] ++ stdenv.lib.optionals doCheck checkInputs;
 
   configureFlags = [
     "--with-pkcs11-config=$$out/etc/pkcs11/" # installation directories
     "--with-pkcs11-modules=$$out/lib/pkcs11/"
   ];
 
+  postPatch = ''
+    patchShebangs build
+  '';
+
+  doCheck = true;
+  checkPhase = ''
+    export HOME=$(mktemp -d)
+    dbus-run-session \
+      --config-file=${dbus.daemon}/share/dbus-1/session.conf \
+      make check
+  '';
+
   meta = with stdenv.lib; {
-    platforms = platforms.linux;
+    description = "Collection of components in GNOME that store secrets, passwords, keys, certificates and make them available to applications";
+    homepage = https://wiki.gnome.org/Projects/GnomeKeyring;
+    license = licenses.gpl2;
     maintainers = gnome3.maintainers;
+    platforms = platforms.linux;
   };
 }