treewide: migrate to pythonPackages.unittestCheckHook

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

@@ -1,4 +1,4 @@
-{ lib, buildPythonPackage, fetchPypi, python }:
+{ lib, buildPythonPackage, fetchPypi, unittestCheckHook }:
 
 buildPythonPackage rec {
   pname = "pytz";
@@ -9,9 +9,9 @@ buildPythonPackage rec {
     sha256 = "sha256-HnYOL+aoFjvAs9mhnE+ENCr6Cir/6/qoSwG5eKAuyqc=";
   };
 
-  checkPhase = ''
-    ${python.interpreter} -m unittest discover -s pytz/tests
-  '';
+  checkInputs = [ unittestCheckHook ];
+
+  unittestFlagsArray = [ "-s" "pytz/tests" ];
 
   pythonImportsCheck = [ "pytz" ];