anchor.diff:  
     ${vamImpl}
     ${pathogenImpl}
  +  ${plugImpl}
     ${vundleImpl}
     ${neobundleImpl}
     ${nativeImpl}
  
positive.code:     packages ? {},
      givenKnownPlugins ? null,
      vam ? null,
      pathogen ? null, ...
    }:
      let
        # This is probably overcomplicated, but I don't understand this well enough to know what's necessary.
  
negative.code:     vimrcConfig.pathogen.pluginNames = [ "vim-addon-nix" ];
    };
  
    test_vim_with_vim_addon_nix_using_plug = vim_configurable.customize {
      name = "vim-with-vim-addon-nix-using-plug";
      vimrcConfig.plug.plugins = with vimPlugins; [ vim-addon-nix ];
    };
  
    test_vim_with_vim_addon_nix = vim_configurable.customize {
      name = "vim-with-vim-addon-nix";
      vimrcConfig.packages.myVimPackage.start = with vimPlugins; [ vim-addon-nix ];
  