bpo-42142: Skip select ttk tests when on Ubuntu

[E-Paine]

Note: This is only designed as a temporary solution to avoid the inconvenience inevitably caused to other (unrelated) PRs.

Note: This will apply (I believe) for all Ubuntu machines (it will certainly affect Azure Pipelines, Travis CI & the Github Action)

https://bugs.python.org/issue42142

[E-Paine]

@terryjreedy or @serhiy-storchaka would you mind please reviewing this PR which will skip the LabeledScaleTest.test_resize and ComboboxTest.test_virtual_event tests when on Ubuntu. As noted, this is only designed as a temporary fix until a more permanent solution for the failures is found.

[tiran]

Nice hack 👍

Too bad we don't have os-release support in the platform module. I had a working patch but I closed it after I was harassed by systemd haters.

[E-Paine]

@serhiy-storchaka please could you review this PR or at least give feedback on the approach used because this issue is clearly annoying others (hence @tiran's report of it)

[serhiy-storchaka]

I do not like that tests are always skipped on Ubuntu. They are passed successfully on my computer, why should they be skipped?

[E-Paine]

They are passed successfully on my computer, why should they be skipped?

Because, as far as I can tell, we cannot distinguish between the bots and a 'real' machine. This disabled it on the relevant bots while trying to keep the skips to as small a number of machines as possible (that's why they are skipped on Ubuntu rather than Linux). I agree it is a shame to affect perfectly good machines, and am open to other solutions, but the only other (that doesn't skip the relevant tests) I could come up with was to use threads to timeout wait_visibility gracefully after a second or so.

[tiran]

I added a parser for freedesktop.org os-release in #23492 . You can use the feature to properly identify Ubuntu and its derivatives: info["ID"] == "ubuntu" or "ubuntu" in info.get("ID_LIKE", ())