Delay creating a test suite inside DiscoverRunner.build_suite()

[Chris Jerdonek]

I noticed that ​DiscoverRunner.build_suite() internally uses a test suite to successively build up its test suite return value. However, build_suite() could be simplified slightly by using a list internally and creating the suite only later towards the end.

One benefit of this is that two of the helper functions that build_suite() calls, namely filter_tests_by_tags() and reorder_suite(), could be updated to operate on simple lists. This would reduce the amount of code that needs to know about test suites and their special handling.

For example, filter_tests_by_tags() could change from this:

def filter_tests_by_tags(suite, tags, exclude_tags):
    suite_class = type(suite)
    return suite_class(
        test for test in iter_test_cases(suite)
        if test_match_tags(test, tags, exclude_tags)
    )

to this:

def filter_tests_by_tags(tests, tags, exclude_tags):
    return [test for test in tests if test_match_tags(test, tags, exclude_tags)]

[Mariusz Felisiak <felisiak.mariusz@…>]

In d828beb6:

Fixed #32529 -- Delayed creating a test suite in build_suite().