python3.pkgs.hyperkitty: use checkInputs

The previously propagated build inputs are optional, and so are
included in checkInputs so the tests can run, but not propagated so
they aren't included if unneeded.

pkgs/servers/mail/mailman/hyperkitty.nix

@@ -15,14 +15,19 @@ buildPythonPackage rec {
   };
 
   nativeBuildInputs = [ isort ];
-  buildInputs = [ coverage mock ];
   propagatedBuildInputs = [
     robot-detection django_extensions rjsmin cssmin django-mailman3
     django-haystack flufl_lock networkx dateutil defusedxml
     django-paintstore djangorestframework django django-q
-    django_compressor beautifulsoup4 six psycopg2 whoosh isort elasticsearch
+    django_compressor six psycopg2 isort
   ];
 
+  # Some of these are optional runtime dependencies that are not
+  # listed as dependencies in setup.py.  To use these, they should be
+  # dependencies of the Django Python environment, but not of
+  # HyperKitty so they're not included for people who don't need them.
+  checkInputs = [ beautifulsoup4 coverage elasticsearch mock whoosh ];
+
   checkPhase = ''
     cd $NIX_BUILD_TOP/$sourceRoot
     PYTHONPATH=.:$PYTHONPATH python example_project/manage.py test \