anchor.diff:           cannot_enable_duplicate_module_plugin/1,
            cannot_enable_duplicate_app_plugin/1,
            module_plugin_mod_does_not_exist/1,
  -         module_plugin_function_does_not_exist/1]).
  +         module_plugin_function_does_not_exist/1,
  +         app_plugin_mod_does_not_exist/1,
  +         app_plugin_function_does_not_exist/1]).
   
   -export([sample_hook_function/0,
            sample_hook_function/1,
  
positive.code:     %% but it does not get written to the config file again.
      {plugins, [{module, ?MODULE, [{hooks, [{hookname, sample_hook_function, 0}]}]}]} = read_config(Config).
  
  
  cannot_enable_duplicate_app_plugin(Config) ->
      ok = write_config(Config ,empty_plugin_config()),
      {ok, _} = application:ensure_all_started(vmq_plugin),
      ok = vmq_plugin_mgr:enable_plugin(vmq_plugin, [code:lib_dir(vmq_plugin)]),
      {error,already_enabled} = vmq_plugin_mgr:enable_plugin(vmq_plugin, [code:lib_dir(vmq_plugin)]).
  
  module_plugin_function_does_not_exist(Config) ->
      ok = write_config(Config ,empty_plugin_config()),
  
negative.code:      cannot_enable_duplicate_module_plugin,
       cannot_enable_duplicate_app_plugin,
       module_plugin_mod_does_not_exist,
       module_plugin_function_does_not_exist,
       app_plugin_mod_does_not_exist,
       app_plugin_function_does_not_exist].
  
  init_per_suite(Config) ->
      application:ensure_all_started(lager),
  