anchor.diff: -{ lib
  +{ stdenv
   , buildPythonPackage
   , fetchPypi
   , pythonOlder
  
positive.code: 
    pythonImportsCheck = [ "jupyterlab_git" ];
  
    meta = with lib; {
      description = "Jupyter lab extension for version control with Git.";
      license = with licenses; [ bsd3 ];
      homepage = "https://github.com/jupyterlab/jupyterlab-git";
  
negative.code: 
    propagatedBuildInputs = [ notebook nbdime git ];
  
    # all Tests on darwin fail or are skipped due to sandbox
    doCheck = !stdenv.isDarwin;
  
    checkInputs = [ pytest ];
  
    checkPhase = ''
  