Added runtests.py support for directory path test labels.

[Chris Jerdonek]

I noticed that runtests.py does its own rudimentary "parsing" of the provided test labels here:
​https://github.com/django/django/blob/548dce50cf548e777a0c34b5485a146a0606ae73/tests/runtests.py#L128-L132

However, it would be better if it used the same logic as DiscoverRunner.build_suite():
​https://github.com/django/django/blob/548dce50cf548e777a0c34b5485a146a0606ae73/django/test/runner.py#L612

There are a few reasons for this. First, it would let runtests take into account the test tags when determining which app modules apply. Second, it would centralize the test label logic, which should simplify maintenance. (For example, I was previously unaware of this code path, which explains why some things mysteriously weren't working before.) Third, it might even permit test labels to be directory paths when used with runtests.py, as a free side effect. (Currently, directory paths don't seem to work with runtests.py, I believe for this reason.) A fourth is that runtests.py will fail faster if a bad test label is passed.

[Chris Jerdonek]

Here is a first PR: ​https://github.com/django/django/pull/14276

I want to wait until #32611 is resolved before doing more because there is overlap, but this is a good change to make in isolation.

[GitHub <noreply@…>]

In 413c15ef:

Refs #32609 -- Simplified test_labels_set construction in runtests.py's setup().

Follow up to 7cf3a5786bc76374e743fbc0c1a1c8470a61f6c0.

[Chris Jerdonek]

PR: ​https://github.com/django/django/pull/14507

This PR isn't the approach I had planned when filing this ticket, but it achieves the main part of what I was after, which is this part of my original comment:

Third, it might even permit test labels to be directory paths when used with runtests.py, as a free side effect. (Currently, directory paths don't seem to work with runtests.py, I believe for this reason.)

In other words, it fixes this issue that Carlton encountered when running runtests.py: ​https://github.com/django/django/pull/14180#pullrequestreview-624099857

As for the rest of the points, I'm not sure any longer if it's possible or desirable to call DiscoverRunner.build_suite()'s logic from within runtests.py. The reason is that there's a bootstrapping issue: To load tests you need to do runtests.py's setup, but to do runtests.py's setup, you first have to know what the needed test modules are. This is after developing a better understanding of runtests.py in the course of working on #32668.

[Mariusz Felisiak <felisiak.mariusz@…>]

In de4f620:

Fixed #32609 -- Updated runtests.py to support directory path test labels.

For example, with this change, the following now works from the tests
directory:

$ ./runtests.py view_tests/tests/