We neither merge nor error when PYTEST_ADDOPTS is specified in user config.

[jsirois]

A user found when they ran certain tests, this was logged:

[WARN] Failed to generate JUnit XML data for test/python/...

Those tests have a BUILD of:

python_tests(
    name="tests",
    dependencies=[
        "3rdparty/python:nautobot-plugin-reqs",
        "3rdparty/python:reqs#pytest-django",
        "src/python/nautobot_animal_sounds",
        "src/python/netops_nautobot",
        "src/python/pytest_nautobot",
    ],
    extra_env_vars=[
        "DJANGO_SETTINGS_MODULE=nautobot.core.tests.nautobot_config",
        "NAUTOBOT_CONFIG=./src/python/netops_nautobot/nautobot_config.py",
        "NAUTOBOT_REDIS_PASSWORD=decinablesprewad",
        "PYTEST_ADDOPTS=-p pytest_nautobot --reuse-db",
    ],
    sources=["**/test_*.py"],
)

And we do not guard against PYTEST_ADDOPTS being set by the user; so our communication channel with pytest is stomped:

pants/src/python/pants/backend/python/goals/pytest_runner.py

Lines 315 to 322 in a69b8f0

	extra_env = {
	"PYTEST_ADDOPTS": " ".join(add_opts),
	"PEX_EXTRA_SYS_PATH": ":".join(prepared_sources.source_roots),
	**test_extra_env.env,
	# NOTE: field_set_extra_env intentionally after `test_extra_env` to allow overriding within
	# `python_tests`.
	**field_set_extra_env,
	}

[erjac77]

I'm on it!