How to use temporary directories and files in tests

The tmp_path fixture

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-6.x.y, py-1.x.y, pluggy-1.x.y
cachedir: .pytest_cache
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 =============================

The tmp_path_factory fixture

The 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.

The tmpdir and tmpdir_factory fixtures

The tmpdir and tmpdir_factory fixtures are similar to tmp_path and tmp_path_factory, but use/return legacy py.path.local objects rather than standard pathlib.Path objects. These days, prefer to use tmp_path and tmp_path_factory.

See tmpdir tmpdir_factory API for details.

The default base temporary directory

Temporary directories are by default created as sub-directories of the system temporary directory. The base name will be pytest-NUM where NUM will be incremented with each test run. Moreover, entries older than 3 temporary directories will be removed.

You can override the default temporary directory setting like this:

pytest --basetemp=mydir

Warning

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.