[Qt] Add PasswordInput widget for Qt.

[corranwebster]

This implements the PasswordInput widget for the Qt backend.

See #3914.

Still to-do:

• Change log entry.
• Screenshot for docs.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[corranwebster]

Looks like there is an issue with undo/redo. With manual testing it looks like QLineEdit:

• undo always clears the field
• redo doesn't do anything

This probably makes some sense from a security point of view. Not sure the best way to proceed: in principle it should be possible to subclass QLineEdit and make undo/redo match the behaviour expected in the test, but that seems like a lot of work for a corner case.

The other approach would be to somehow adjust the Testbed test.

[corranwebster]

Requesting review for guidance on best way to handle undo/redo test error.

[freakboy3742]

Thanks for the PR - this looks awesome!

Regarding the undo/redo failure - the general approach here is to try and capture the high level idea that is causing an inconsistency in the test, encode that as a property of the probe, and then make the test conditional on the probe property.

In this case, you might add a property like redo_enabled; this will be True for the TextInput probe, but False for the PasswordInput probe. That way you can test the undo behaviour, but put the redo behavior behind an if probe.redo_enabled: check - possibly also checking the empty content for disabled redos.

The other way it could be tackled would be to make the probe raise pytest.xfail() on a property that is accessed as part of the test. That isn't the best match here, as the value can be retrieved; but in a case where the test is hitting a probe capability that is only used by that test, or can't be implemented at all, it's a handy approach to know about.

The other TODO is the screenshot; the examples folder contains a screenshot app; if you run that app, it will generate screenshots for all the currently enabled widgets. Rename appropriately and put in the docs folder, and this should be pretty close to done!

[freakboy3742]

I see from your other PR (#3959) that you might not be in a position to generate the screenshot; if that's the case, let me know - I can generate that and add it to your PR prior to landing.

[freakboy3742]

I've just added a screenshot for you.

[corranwebster]

@freakboy3742 I think this is ready for re-review.

As suggested, I've added a redo_available flag for the undo/redo test which changes the expected results when undo/redo is tested on text-based widgets.

[freakboy3742]

Another great contribution - thanks!