foo.test_foo is imported twice, including once before running conftest, when using pytest --pyargs foo.test_foo #5078
Description
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foo.test_foo is imported twice, including once before running conftest, when using pytest --pyargs foo.test_foo.
Python 3.7 / Arch Linux
$ pip list
Package Version
-------------- -------
atomicwrites 1.3.0
attrs 19.1.0
more-itertools 7.0.0
pip 19.0.3
pluggy 0.9.0
py 1.8.0
pytest 4.4.0
setuptools 40.8.0
six 1.12.0
$ tree
.
└── foo
├── conftest.py
├── __init__.py
└── test_foo.py
$ cat foo/conftest.py
def pytest_configure(config):
print("configuring")
$ cat foo/test_foo.py
print("in test_foo")
def test_1(): pass
$ pytest --pyargs foo.test_foo -s
===================================== test session starts ======================================
platform linux -- Python 3.7.3, pytest-4.4.0, py-1.8.0, pluggy-0.9.0
rootdir: /tmp/foo
collecting ... in test_foo
configuring
in test_foo
collected 1 item
foo/test_foo.py .
=================================== 1 passed in 0.01 seconds ===================================
Note that "in test_foo" appears twice, including once before the call to pytest_configure (which prints out "configuring").
This means that if test_foo has toplevel logic that depends on pytest_configure (e.g., via https://docs.pytest.org/en/latest/example/simple.html#detect-if-running-from-within-a-pytest-run -- an example is matplotlib's test helpers, which has a decorator to either generate a pytest test or a nose test instance), the logic will be wrong -- even though the test collected "pre-configure" will actually be discarded later (this happens in collect_one_node in _perform_collect), this can still e.g. trigger spurious warnings from toplevel code.