python.pkgs.backports_lzma: fix tests

pkgs/development/python-modules/backports_lzma/default.nix

@@ -20,9 +20,8 @@ if !(pythonOlder "3.3") then null else buildPythonPackage rec {
 
   buildInputs = [ lzma ];
 
-  # Needs the compiled module in $out
   checkPhase = ''
-    PYTHONPATH=$out/${python.sitePackages}:$PYTHONPATH ${python.interpreter} -m unittest discover -s test
+    ${python.interpreter} test/test_lzma.py
   '';
 
   meta = {
@@ -30,4 +29,4 @@ if !(pythonOlder "3.3") then null else buildPythonPackage rec {
     homepage = https://github.com/peterjc/backports.lzma;
     license = lib.licenses.bsd3;
   };
-}
+}