test: switch from sphinx-testing @with_app to sphinx.application.Sphinx

[jnikula]

The sphinx-testing package that provides the handy @with_app decorator has been deprecated in favour of sphinx.testing for years.

The sphinx.testing package provides a make_app pytest fixture to create a test app, but there are a number of downsides with it:

• You can only use make_app as a pytest fixture, and for test functions only. In our case, we'd have to route make_app as a parameter from test_directive_*() via testcase.run_test() all the way to the get_output() and get_expected() methods.

• There's no automatic temp directory creation and deletion for srcdir.

• There's no confdir parameter, so conf.py needs to be copied.

• It forces you to use the weird sphinx.testing custom path class.

I fail to see the upsides of jumping through hoops to use sphinx.testing for testing. Turns out it's actually much more clear to use sphinx.application.Sphinx directly. A lot of the "helpful" parts that make_app provides turn out to be something that we'd need to work around, and the Sphinx app lets us clean up things that were needed because of @with_app.

Use sphinx.application.Sphinx directly for Sphinx build.

[BrunoMSantos]

Hmm, when I looked at it I got the impression it would be tricky to convert, but this is pretty simple. Looks good to me ;)

Sorry I only got around to it now.

[jnikula]

Hmm, when I looked at it I got the impression it would be tricky to convert, but this is pretty simple. Looks good to me ;)

It would've been tricky to convert to sphinx.testing! Just using the actual Sphinx app directly was much easier.

Sorry I only got around to it now.

No worries, and thanks!