anchor.diff:  -spec mock(Opts) -> ok when
       Opts :: [Option],
       Option :: {update, [App]}
  +            | {cache_dir, string()}
               | {default_vsn, Vsn}
               | {override_vsn, [{App, Vsn}]}
               | {not_in_index, [{App, Vsn}]}
  
positive.code:                 [kernel, stdlib] ++ [element(1,D) || D  <- AppDeps]
              ),
              rebar_test_utils:create_config(Dir, [{deps, AppDeps}]),
              Tarball = filename:join([Dir, App++"-"++binary_to_list(Vsn)++".tar"]),
              Contents = filename:join([Dir, "contents.tar.gz"]),
              Files = all_files(rebar_app_info:dir(AppInfo)),
              ok = erl_tar:create(Contents,
  
negative.code:             ok = erl_tar:create(Tarball,
                                  [{"contents.tar.gz", Contents}],
                                  []),
              Cache = proplists:get_value(cache_dir, Opts, filename:join(Dir,"cache")),
              Cached = filename:join([Cache, TarApp]),
              filelib:ensure_dir(Cached),
              rebar_file_utils:mv(Tarball, Cached),
              {ok, true}
          end).
  
  %% @doc On top of the pkg resource mocking, we need to mock the package
  