Contributing to testtools

Bugs and patches

File bugs <> on Launchpad, and send patches <> on Github.

Coding style

In general, follow PEP 8 except where consistency with the standard library’s unittest module would suggest otherwise.

testtools currently supports Python 2.7 and Python 3.4 and later.


All code that is not copyright assigned to Jonathan M. Lange (see Copyright Assignment above) needs to be licensed under the MIT license that testtools uses, so that testtools can ship it.


Building and installing testtools requires a reasonably recent version of pip. At the time of writing, pip version 7.1.0 (which is bundled with virtualenv 13.1.0) is a good choice. To install testtools from source and all its test dependencies, install the test extra:

pip install -e .[test]

Installing via python install may not work, due to issues with easy_install.


Please write tests for every feature. This project ought to be a model example of well-tested Python code!

Take particular care to make sure the intent of each test is clear.

You can run tests with make check.

By default, testtools hides many levels of its own stack when running tests. This is for the convenience of users, who do not care about how, say, assert methods are implemented. However, when writing tests for testtools itself, it is often useful to see all levels of the stack. To do this, add run_tests_with = FullStackRunTest to the top of a test’s class definition.


When submitting a patch, it will help the review process a lot if there’s a clear explanation of what the change does and why you think the change is a good idea. For crasher bugs, this is generally a no-brainer, but for UI bugs & API tweaks, the reason something is an improvement might not be obvious, so it’s worth spelling out.

If you are thinking of implementing a new feature, you might want to have that discussion on the [mailing list]( before the patch goes up for review. This is not at all mandatory, but getting feedback early can help avoid dead ends.


Documents are written using the Sphinx variant of reStructuredText. All public methods, functions, classes and modules must have API documentation. When changing code, be sure to check the API documentation to see if it could be improved. Before submitting changes to trunk, look over them and see if the manuals ought to be updated.

Source layout

The top-level directory contains the testtools/ package directory, and miscellaneous files like README.rst and

The testtools/ directory is the Python package itself. It is separated into submodules for internal clarity, but all public APIs should be “promoted” into the top-level package by importing them in testtools/ Users of testtools should never import a submodule in order to use a stable API. Unstable APIs like testtools.matchers and testtools.deferredruntest should be exported as submodules.

Tests belong in testtools/tests/.

Committing to trunk

Testtools is maintained using git, with its master repo at This gives every contributor the ability to commit their work to their own branches. However permission must be granted to allow contributors to commit to the trunk branch.

Commit access to trunk is obtained by joining the testing-cabal, either as an Owner or a Committer. Commit access is contingent on obeying the testtools contribution policy, see Copyright Assignment above.

Code Review

All code must be reviewed before landing on trunk. The process is to create a branch on Github, and make a pull request into trunk. It will then be reviewed before it can be merged to trunk. It will be reviewed by someone:

  • not the author
  • a committer

As a special exception, since there are few testtools committers and thus reviews are prone to blocking, a pull request from a committer that has not been reviewed after 24 hours may be merged by that committer. When the team is larger this policy will be revisited.

Code reviewers should look for the quality of what is being submitted, including conformance with this HACKING file.

Changes which all users should be made aware of should be documented in NEWS.

We are now in full backwards compatibility mode - no more releases < 1.0.0, and breaking compatibility will require consensus on the testtools-dev mailing list. Exactly what constitutes a backwards incompatible change is vague, but coarsely:

  • adding required arguments or required calls to something that used to work
  • removing keyword or position arguments, removing methods, functions or modules
  • changing behaviour someone may have reasonably depended on

Some things are not compatibility issues:

  • changes to _ prefixed methods, functions, modules, packages.

NEWS management

The file NEWS is structured as a sorted list of releases. Each release can have a free form description and more or more sections with bullet point items. Sections in use today are ‘Improvements’ and ‘Changes’. To ease merging between branches, the bullet points are kept alphabetically sorted. The release NEXT is permanently present at the top of the list.



Membership in the testing-cabal org on github as committer.

Membership in the pypi testtools project as maintainer.

Membership in the

No in-progress Critical bugs on the next milestone.


  1. Choose a version number, say X.Y.Z
  2. Under NEXT in NEWS add a heading with the version number X.Y.Z.
  3. Possibly write a blurb into NEWS.
  4. Commit the changes.
  5. Tag the release, git tag -s X.Y.Z -m "Releasing X.Y.Z"
  6. Run ‘make release’, this: #. Creates a source distribution and uploads to PyPI #. Ensures all Fix Committed bugs are in the release milestone #. Makes a release on Launchpad and uploads the tarball #. Marks all the Fix Committed bugs as Fix Released #. Creates a new milestone
  7. If a new series has been created (e.g. 0.10.0), make the series on Launchpad.
  8. Push trunk to Github, git push --tags origin master