`test_warnings` fails if run with `-Werror`

[AlexWaygood]

Bug report

Bug description:

./python.exe -Werror -m test test_warnings fails, which feels sort-of ironic:

~/dev/cpython (main)⚡ % ./python.exe -We -m test test_warnings
Using random seed: 673638140
Raised RLIMIT_NOFILE: 256 -> 1024
0:00:00 load avg: 2.83 Run 1 test sequentially in a single process
0:00:00 load avg: 2.83 [1/1] test_warnings
test test_warnings failed -- Traceback (most recent call last):
  File "/Users/alexw/dev/cpython/Lib/test/test_warnings/__init__.py", line 904, in test_issue31285
    wmod.warn_explicit(
    ~~~~~~~~~~~~~~~~~~^
        'foo', UserWarning, 'bar', 1,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        module_globals={'__loader__': get_bad_loader(42),
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        '__name__': 'foobar'})
                        ^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap_external>", line 934, in _bless_my_loader
DeprecationWarning: Module globals is missing a __spec__.loader

test_warnings failed (1 error)

== Tests result: FAILURE ==

1 test failed:
    test_warnings

Total duration: 482 ms
Total tests: run=146
Total test files: run=1/1 failed=1
Result: FAILURE

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-122191: Fix test_warnings failure if run with -Werror #122222
• [3.13] gh-122191: Fix test_warnings failure if run with -Werror (GH-122222) #122256
• [3.12] gh-122191: Fix test_warnings failure if run with -Werror (GH-122222) #122257

[x0rw]

Well, I spent some time tracking the error back to '/**/cpython/cpython/Lib/importlib/_bootstrap_external.py' at "_bless_my_loader," where it checks if the module globals contain loader or spec. At line 935, it raises a warning:

_warnings.warn(
    'Module globals is missing a __spec__.loader',
    DeprecationWarning
)

Since test_warning tests warnings, it doesn't make sense to run it with --Werror, which treats warnings as errors.
so a possible solution is to check if there is -Werror in args when runing warning tests

[serhiy-storchaka]

In future, warnings will be turned into errors. Unless we are planning to remove these tests, the warnings should not be ignored.