anchor.diff:      {error, already_stopped} = stop().
   
   sum_areas_test() ->
  +    Shapes = [{circle, 0.3}],
       {ok, _Pid} = start(),
  -    Shapes = [{circle, 0.3}],
  +
       Client = spawn(fun() ->
   			   receive
   			       {reply, {sum_areas, ok, Sum}} ->
  
positive.code:     {ok, stopped} = stop().
  
  timeout_test() ->
      {ok, _Pid} = start(),
      Shapes = [{circle, 3}],
      stop(),
      Client = spawn(fun() -> receive Reply -> ?assertEqual({'EXIT', timeout}, Reply) after 4 -> exit(timeout) end end),
  
  
negative.code:     {error, already_stopped} = stop().
  
  sum_areas_unknown_shapes_test() ->
      Shapes = [{ellipse, 3, 6}],
      {ok, _Pid} = start(),
  
      Client = spawn(fun() -> receive
  				Reply ->
  				    ?assertMatch({reply, {sum_areas, {error, {function_clause, _Detail}}}}, Reply)
  