The CompletionView looks in objreg for 'status-cmd', so move it from a
private fixture in test_completer to a public fixture that handles
objreg registration/deletion.
update_completion is only used internally, so instead test the real
public entry point which is schedule_completion_update.
This required mocking out QTimer to fire immediately so the test didn't
have to do flaky artificial delays.
For the Completer unit tests:
Although `change_completed_part` looks like a public method, it was
only used internally. Test the externally-used method
`selection_changed` instead.
Based on code review:
- Use qtbot.waitSignal to test a signal firing
- Use pytest.mark.xfail for an expected test failure
- Ensure there are 2 newlines between module-level functions
Based on code review:
- import modules, not classes
- use methods, not lambdas for the mock command prompt class
- use None rather than Mock for DUMB_SORT
- autouse two fixtures and remove them from test signatures
