Skip to content


Switch branches/tags

Latest commit

- rmdir and chmod work without permission
  if the file user ID is the current user ID
- better handle owner/group/other permission bits
- fixes #719

Git stats


Failed to load latest commit information.
Latest commit message
Commit time

pyfakefs PyPI version Python version Testsuite

pyfakefs implements a fake file system that mocks the Python file system modules. Using pyfakefs, your tests operate on a fake file system in memory without touching the real disk. The software under test requires no modification to work with pyfakefs.

pyfakefs works with Linux, Windows and MacOS.

pyfakefs provides the fs fixture for use with pytest, which will automatically invoke the fake filesystem. It also provides the fake_filesystem_unittest.TestCase class for use with unittest and the means to use the fake filesystem with other test frameworks.


This file provides general usage instructions for pyfakefs. There is more:


The simplest method to use pyfakefs is using the fs fixture with pytest. Refer to the usage documentation for information on other test scenarios, test customization and using convenience functions.


pyfakefs works with CPython 3.7 and above, on Linux, Windows and OSX (MacOS), and with PyPy3.

pyfakefs works with pytest version 3.0.0 or above, though a current version is recommended.

pyfakefs will not work with Python libraries that use C libraries to access the file system. This is because pyfakefs cannot patch the underlying C libraries' file access functions--the C libraries will always access the real file system. For example, pyfakefs will not work with lxml. In this case lxml must be replaced with a pure Python alternative such as xml.etree.ElementTree.


Continuous integration

pyfakefs is currently automatically tested on Linux, MacOS and Windows, with Python 3.7 to 3.11, and with PyPy3 on Linux, using GitHub Actions.

Running pyfakefs unit tests

On the command line

pyfakefs unit tests can be run using pytest (all tests) or unittest (all tests except pytest-specific ones):

$ cd pyfakefs/

$ python -m pytest pyfakefs
$ python -m pyfakefs.tests.all_tests

Similar scripts are called by tox and Github Actions. tox can be used to run tests locally against supported python versions:

$ tox

In a Docker container

The Dockerfile at the repository root will run the tests on the latest Ubuntu version. Build the container:

cd pyfakefs/
docker build -t pyfakefs .

Run the unit tests in the container:

docker run -t pyfakefs

Contributing to pyfakefs

We always welcome contributions to the library. Check out the Contributing Guide for more information.

History was initially developed at Google by Mike Bland as a modest fake implementation of core Python modules. It was introduced to all of Google in September 2006. Since then, it has been enhanced to extend its functionality and usefulness. At last count, pyfakefs was used in over 2,000 Python tests at Google.

Google released pyfakefs to the public in 2011 as Google Code project pyfakefs:

After the shutdown of Google Code was announced, John McGehee merged all three Google Code projects together here on GitHub where an enthusiastic community actively supports, maintains and extends pyfakefs.


pyfakefs implements a fake file system that mocks the Python file system modules.







No packages published