python3Packages.purl: propagate six, add import check

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

@@ -1,4 +1,7 @@
-{ lib, buildPythonPackage, fetchFromGitHub
+{ lib
+, buildPythonPackage
+, fetchFromGitHub
+, six
 , pytestCheckHook
 }:
 
@@ -13,7 +16,17 @@ buildPythonPackage rec {
     sha256 = "sha256-Jb3JRW/PtQ7NlO4eQ9DmTPu/sjvFTg2mztphoIF79gc=";
   };
 
-  checkInputs = [ pytestCheckHook];
+  propagatedBuildInputs = [
+    six
+  ];
+
+  checkInputs = [
+    pytestCheckHook
+  ];
+
+  pythonImportsCheck = [
+    "purl"
+  ];
 
   meta = with lib; {
     description = "Immutable URL class for easy URL-building and manipulation";