anchor.diff:  # This test start mongodb, runs a query using mongo shell
   
  -import ./make-test.nix ({ pkgs, ... }:
  +import ./make-test-python.nix ({ pkgs, ... }:
     let
       testQuery = pkgs.writeScript "nixtest.js" ''
         db.greetings.insert({ "greeting": "hello" });
  
positive.code:       };
      };
  
      testScript = "$node->start;" 
  #      + runMongoDBTest pkgs.mongodb-3_4
        + runMongoDBTest pkgs.mongodb-3_6 
        + runMongoDBTest pkgs.mongodb-4_0
        + "$node->shutdown;";
    })
  
negative.code:     '';
  
      runMongoDBTest = pkg: ''
        node.execute("(rm -rf data || true) && mkdir data")
        node.execute(
            "${pkg}/bin/mongod --fork --logpath logs --dbpath data"
        )
        node.wait_for_open_port(27017)
  
        assert "hello" in node.succeed(
            "mongo ${testQuery}"
        )
  
        node.execute(
            "${pkg}/bin/mongod --shutdown --dbpath data"
        )
        node.wait_for_closed_port(27017)
      '';
  
    in {
  