anchor.diff:  { lib
   , buildPythonPackage
   , pythonOlder
  -, isPy35
  -, isPy36
   , fetchPypi
   , hypothesis
   , pytestcache
  -, pytestcov
   , pytestflakes
   , pytestpep8
   , pytest
  
positive.code:   pname = "natsort";
    version = "5.2.0";
  
    buildInputs = [
      hypothesis
      pytestcache
      pytestcov
      pytestflakes
      pytestpep8
      pytest
  
negative.code:   # testing based on project's tox.ini
    checkPhase = ''
      pytest --doctest-modules natsort
      pytest --flakes --pep8
    '';
  
    meta = {
  