🧪 Start testing under Python 3.14(t) in CI

[webknjaz]

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• Included tests for the changes.
• A change note is created in changelog.d/ (see changelog.d/README.md for instructions) or the PR text says "no changelog needed".

Maintainer checklist

• If no changelog is needed, apply the skip-changelog label.
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[AndydeCleyre]

Outside the scope of this PR, but this commit updating one of the testing packages to use pyproject.toml might be handy when fixing those new failures.

[webknjaz]

Thanks for the ref! AFAICS, old pip + python 3.14 is the combo that fails.

This is what PDB gives me:

tests/test_cli_compile.py::test_editable_package[legacy resolver] FAILED
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> traceback >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

pip_conf = '/tmp/pytest-of-<username>/pytest-19/test_editable_package_legacy_r0/pip.conf', runner = <click.testing.CliRunner object at 0x7fc9c575a200>

    def test_editable_package(pip_conf, runner):
        """piptools can compile an editable"""
        fake_package_dir = os.path.join(PACKAGES_PATH, "small_fake_with_deps")
        fake_package_dir = path_to_url(fake_package_dir)
        with open("requirements.in", "w") as req_in:
            req_in.write("-e " + fake_package_dir)  # require editable fake package
    
        out = runner.invoke(cli, ["-n"])
    
>       assert out.exit_code == 0
E       assert 1 == 0
E        +  where 1 = <Result InstallationError("file://~/src/github/jazzband/pip-tools/tests/test_data/packages/small_fake_with_deps (from -r requirements.in (line 1)) does not appear to be a Python project: neither 'setup.py' nor 'pyproject.toml' found.")>.exit_code

~/src/github/jazzband/pip-tools/tests/test_cli_compile.py:526: AssertionError
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PDB post_mortem >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> ~/src/github/jazzband/pip-tools/tests/test_cli_compile.py(526)test_editable_package()
-> assert out.exit_code == 0
(Pdb) pp out.output
('WARNING: the legacy dependency resolver is deprecated and will be removed in '
 'future versions of pip-tools.\n')
(Pdb) pp out.stderr
('WARNING: the legacy dependency resolver is deprecated and will be removed in '
 'future versions of pip-tools.\n')
(Pdb) pp out.stdout
''
(Pdb) pp out.exception
InstallationError("file://~/src/github/jazzband/pip-tools/tests/test_data/packages/small_fake_with_deps (from -r requirements.in (line 1)) does not appear to be a Python project: neither 'setup.py' nor 'pyproject.toml' found.")
(Pdb) pp out.exc_info
(<class 'pip._internal.exceptions.InstallationError'>,
 InstallationError("file://~/src/github/jazzband/pip-tools/tests/test_data/packages/small_fake_with_deps (from -r requirements.in (line 1)) does not appear to be a Python project: neither 'setup.py' nor 'pyproject.toml' found."),
 <traceback object at 0x7fc9c4931000>)
(Pdb) pp pathlib.Path('requirements.in').read_text()
('-e '
 'file:~/src/github/jazzband/pip-tools/tests/test_data/packages/small_fake_with_deps')

I'm wondering if we should skip this test in broken envs or make actual changes... Or perhaps set a different minimum version of pip for py314.