How to use temporary directories and files in tests¶
You can use the
tmp_path fixture which will
provide a temporary directory unique to the test invocation,
created in the base temporary directory.
tmp_path is a
pathlib.Path object. Here is an example test usage:
# content of test_tmp_path.py CONTENT = "content" def test_create_file(tmp_path): d = tmp_path / "sub" d.mkdir() p = d / "hello.txt" p.write_text(CONTENT) assert p.read_text() == CONTENT assert len(list(tmp_path.iterdir())) == 1 assert 0
Running this would result in a passed test except for the last
assert 0 line which we use to look at values:
$ pytest test_tmp_path.py =========================== test session starts ============================ platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y rootdir: /home/sweet/project collected 1 item test_tmp_path.py F [100%] ================================= FAILURES ================================= _____________________________ test_create_file _____________________________ tmp_path = PosixPath('PYTEST_TMPDIR/test_create_file0') def test_create_file(tmp_path): d = tmp_path / "sub" d.mkdir() p = d / "hello.txt" p.write_text(CONTENT) assert p.read_text() == CONTENT assert len(list(tmp_path.iterdir())) == 1 > assert 0 E assert 0 test_tmp_path.py:11: AssertionError ========================= short test summary info ========================== FAILED test_tmp_path.py::test_create_file - assert 0 ============================ 1 failed in 0.12s =============================
tmp_path_factory is a session-scoped fixture which can be used
to create arbitrary temporary directories from any other fixture or test.
For example, suppose your test suite needs a large image on disk, which is
generated procedurally. Instead of computing the same image for each test
that uses it into its own
tmp_path, you can generate it once per-session
to save time:
# contents of conftest.py import pytest @pytest.fixture(scope="session") def image_file(tmp_path_factory): img = compute_expensive_image() fn = tmp_path_factory.mktemp("data") / "img.png" img.save(fn) return fn # contents of test_image.py def test_histogram(image_file): img = load_image(image_file) # compute and test histogram
See tmp_path_factory API for details.
These days, it is preferred to use
In order to help modernize old code bases, one can run pytest with the legacypath plugin disabled:
pytest -p no:legacypath
This will trigger errors on tests using the legacy paths.
It can also be permanently set as part of the
addopts parameter in the
The default base temporary directory¶
Temporary directories are by default created as sub-directories of
the system temporary directory. The base name will be
NUM will be incremented with each test run.
By default, entries older than 3 temporary directories will be removed.
This behavior can be configured with
option will remove the directory before every run, effectively meaning the temporary directories
of only the most recent run will be kept.
You can override the default temporary directory setting like this:
The contents of
mydir will be completely removed, so make sure to use a directory
for that purpose only.
When distributing tests on the local machine using
pytest-xdist, care is taken to
automatically configure a basetemp directory for the sub processes such that all temporary
data lands below a single per-test run basetemp directory.