anchor.diff:  
   repo_dir(GitReference) ->
       ["docsh-", GitReference].
  +
  +install(RepoDir) ->
  +    ["cd ", RepoDir, "; ./install.sh"].
  +
  +file_exists(File) ->
  +    ["file -E ", File].
  +
  +docsh_works() ->
  +    ["erl -noinput -noshell -eval 'erlang:display(docsh:module_info(module)).' -s erlang halt"].
  
positive.code:     try
          sh(within_container(Name, fetch(archive_url(GitRef), archive_file(GitRef)))),
          sh(within_container(Name, extract(archive_file(GitRef)))),
          ct:pal("last result: ~p", [sh(within_container(Name, ["ls ", repo_dir(GitRef)]))]),
          ct:fail("not implemented yet")
      after
          sh("docker stop " ++ Name)
      end.
  
negative.code: 
  sh(Command) when is_binary(Command) -> sh([Command]);
  sh(Command) ->
      case erlsh:oneliner(?b2l(?il2b(Command))) of
          {done, 0 = Code, Result} = R ->
              get(sh_log) == true andalso sh_log(Command, Code, Result),
              R;
          {done, Code, Result} = R ->
              sh_log(Command, Code, Result),
              ct:fail(R)
      end.
  
  sh_log(Command, Code, Result) ->
      ct:pal("command : ~ts\n"
             "code    : ~p\n"
             "result  : ~ts",
             [Command, Code, Result]).
  
  start_container(Name, Args) ->
      Fdlink = erlsh:fdlink_executable(),
  