That is one approach, of course, but imo pretty incomplete.  A test that is named "test_get_only" presumably would be expected to test __getitem__, not __cmp__.  Confusingly there is still a GetOnly item declared in the module, but it is not used.  Compare to test_len_only, which has a paired LenOnly class and test name.

Either GetOnly should be completely excised from the module and the test renamed to test_cmp_only (alternately test_cmp_err), or the GetOnly class should be fixed as in my patch.