Temporary directories and files

The ‘tmpdir’ fixture

You can use the tmpdir fixture which will provide a temporary directory unique to the test invocation, created in the base temporary directory.

tmpdir is a py.path.local object which offers os.path methods and more. Here is an example test usage:

# content of test_tmpdir.py
import os
def test_create_file(tmpdir):
    p = tmpdir.mkdir("sub").join("hello.txt")
    p.write("content")
    assert p.read() == "content"
    assert len(tmpdir.listdir()) == 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_tmpdir.py
======= test session starts ========
platform linux -- Python 3.5.2, pytest-3.0.7, py-1.4.32, pluggy-0.4.0
rootdir: $REGENDOC_TMPDIR, inifile:
collected 1 items

test_tmpdir.py F

======= FAILURES ========
_______ test_create_file ________

tmpdir = local('PYTEST_TMPDIR/test_create_file0')

    def test_create_file(tmpdir):
        p = tmpdir.mkdir("sub").join("hello.txt")
        p.write("content")
        assert p.read() == "content"
        assert len(tmpdir.listdir()) == 1
>       assert 0
E       assert 0

test_tmpdir.py:7: AssertionError
======= 1 failed in 0.12 seconds ========

The ‘tmpdir_factory’ fixture

New in version 2.8.

The tmpdir_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 tmpdir, you can generate it once per-session to save time:

# contents of conftest.py
import pytest

@pytest.fixture(scope='session')
def image_file(tmpdir_factory):
    img = compute_expensive_image()
    fn = tmpdir_factory.mktemp('data').join('img.png')
    img.save(str(fn))
    return fn

# contents of test_image.py
def test_histogram(image_file):
    img = load_image(image_file)
    # compute and test histogram

tmpdir_factory instances have the following methods:

TempdirFactory.mktemp(basename, numbered=True)[source]

Create a subdirectory of the base temporary directory and return it. If numbered, ensure the directory is unique by adding a number prefix greater than any existing one.

TempdirFactory.getbasetemp()[source]

return base temporary directory.

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

When distributing tests on the local machine, pytest takes care to configure a basetemp directory for the sub processes such that all temporary data lands below a single per-test run basetemp directory.