Added test for on_gain_focus and on_lose_focus

[dgmouris]

Adds a test for on_gain_focus and on_lose_focus

Adds a bit more testing regarding on_lose_focus and on_gain_focus, as I couldn't find them anywhere.

#1601 (perhaps?)

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

[dgmouris]

Just thought this might be a small help, I came into something on a personal project on losing focus so I thought I'd add a test just for my own peace of mind. If it's not relevant that's fine too!

Don't think there's anything to document here, but I might be wrong.

I'll add the change so towncrier passes shortly.

[freakboy3742]

Thanks for the suggestion; however in this case, it's already being tested! test_textinput.py imports test_focus from the base property tests, which validates the on_gain_focus and on_lose_focus signals.

This is a general pattern that is followed by a lot of widgets - since the underlying test for focus is fundamentally the same, we can use the same test repeatedly, just replacing the widget that is used as a fixture for that test.

In terms of #1600 and coverage - we're almost there. #2075 is the last PR of the widget audit, and part of that PR is turning on the "fail the test suite if there isn't 100% branch coverage" test condition on both the core and the testbed. As I write this, the core, plus iOS and GTK backends have 100% coverage, macOS backend is currently failing because of 1 line of missing coverage (although this should be corrected in an hour or two).

Closing on the basis that the PR isn't required, but thanks for the effort anyway!

[dgmouris]

Thank you for the kind comment, my apologies on this!