anchor.diff:  
   %%--------------------------------------------------------------------
   %% @doc
  -%% Removes a user (owner of auth) from space users list.
  +%% Removes a user (owner of auth) from group users list.
   %% @end
   %%--------------------------------------------------------------------
   -spec leave_group(oz_endpoint:client(), GroupId :: binary()) ->
  
positive.code: 
  %%--------------------------------------------------------------------
  %% @doc
  %% Returns list of user space IDs.
  %% @end
  %%--------------------------------------------------------------------
  -spec get_groups(oz_endpoint:client(), UserId :: onedata_user:id()) ->
  
negative.code: 
  %%--------------------------------------------------------------------
  %% @doc
  %% Adds a user (owner of auth) to a group.
  %% @end
  %%--------------------------------------------------------------------
  -spec join_group(oz_endpoint:client(), GroupId :: binary()) ->
  