pythonPackages.traitlets: fix tests

pkgs/top-level/python-packages.nix

···
       sha256 = "ba8c94323ccbe8fd792e45d8efe8c95d3e0744cc8c085295b607552ab573724c";
     };
 
-    buildInputs = with self; [ nose mock ];
-    propagatedBuildInputs = with self; [ipython_genutils decorator];
+    LC_ALL = "en_US.UTF-8";
+
+    buildInputs = with self; [ pkgs.glibcLocales pytest mock ];
+    propagatedBuildInputs = with self; [ipython_genutils decorator enum34];
 
     checkPhase = ''
-      nosetests -v
+      py.test $out
     '';
 
     meta = {