test_do_not_import_files_from_local_directory fails with trying to import "completely_unknown"

[bnavigator]

(Same environment as in #3635)

Trying to update the openSUSE package for pylint:

[    5s] ============================= test session starts ==============================
[    5s] platform linux -- Python 3.8.2, pytest-5.3.5, py-1.8.1, pluggy-0.13.1 -- /usr/bin/python3
[    5s] cachedir: .pytest_cache
[    5s] benchmark: 3.2.3 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
[    5s] rootdir: /home/abuild/rpmbuild/BUILD/pylint-2.5.2, inifile: pytest.ini
[    5s] plugins: forked-1.1.3, xdist-1.32.0, benchmark-3.2.3
[    7s] collecting ... collected 1404 items / 194 deselected / 1210 selected
...
[  151s] ___________ TestRunTC.test_do_not_import_files_from_local_directory ____________
[  151s] 
...
[  151s]             if check and retcode:
[  151s] >               raise CalledProcessError(retcode, process.args,
[  151s]                                          output=stdout, stderr=stderr)
[  151s] E               subprocess.CalledProcessError: Command '['/usr/bin/python3', '-m', 'pylint', 'astroid.py', '--disable=import-error,unused-import']' returned non-zero exit status 1.
[  151s] 
[  151s] /usr/lib64/python3.8/subprocess.py:512: CalledProcessError
[  151s] ----------------------------- Captured stderr call -----------------------------
[  151s] Traceback (most recent call last):
[  151s]   File "/usr/lib64/python3.8/runpy.py", line 193, in _run_module_as_main
[  151s]     return _run_code(code, main_globals, None,
[  151s]   File "/usr/lib64/python3.8/runpy.py", line 86, in _run_code
[  151s]     exec(code, run_globals)
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/__main__.py", line 18, in <module>
[  151s]     pylint.run_pylint()
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/__init__.py", line 19, in run_pylint
[  151s]     from pylint.lint import Run as PylintRun
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/lint/__init__.py", line 75, in <module>
[  151s]     from pylint.lint.check_parallel import check_parallel
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/lint/check_parallel.py", line 7, in <module>
[  151s]     from pylint import reporters
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/reporters/__init__.py", line 24, in <module>
[  151s]     from pylint import utils
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/utils/__init__.py", line 46, in <module>
[  151s]     from pylint.utils.ast_walker import ASTWalker
[  151s]   File "/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages/pylint/utils/ast_walker.py", line 6, in <module>
[  151s]     from astroid import nodes
[  151s]   File "/tmp/pytest-of-abuild/pytest-57/test_do_not_import_files_from_0/astroid.py", line 2, in <module>
[  151s]     import completely_unknown
[  151s] ModuleNotFoundError: No module named 'completely_unknown'

What could cause the undesired import? If I chroot into the build environment and call
python3 -m pylint astroid.py, I get the same ModuleNotFoundError.

But if I install the package onto a live openSUSE Tumbleweed system and execute the same call, the import does not happen.

Package versions:

python3-astroid-2.4.1
python3-isort-4.3.21
python3-mccabe-0.6.1
python3-toml-0.10.0

For the full environment, see the build log as linked above.

[bnavigator]

Ha! Found it.

PYTHONPATH is set by the %pytest rpm macro to :/home/abuild/rpmbuild/BUILDROOT/python-pylint-2.5.2-0.x86_64/usr/lib/python3.8/site-packages. The leading ":" means the effective sys.path is ['', cwd, ...] and then the code https://github.com/PyCQA/pylint/blob/1fc490c0a1d0df5d4d6a64da0ccf2dd711b9bf67/pylint/__main__.py#L15-L16 does not strip the second entry.