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Don't Panic

The Hypothesis test suite is large, but we've written these notes to help you out. It's aimed at contributors (new and old!) who know they need to add tests somewhere, but aren't sure where - or maybe need some hints on what kinds of tests might be useful. Others might just be interested in how a testing library tests itself!

The very short version

  • To improve code coverage (eg because make check-coverage or CI is failing), go to cover/
  • For longer / system / integration tests, look in nocover/
  • For tests that require an optional dependency, look in the directory named for that dependency.


If you get stuck, just ask a maintainer to help out by mentioning @HypothesisWorks/hypothesis-python-contributors on GitHub. We'd love to help - and also get feedback on how this document could be better!

Some scenarios

I'm adding or changing a strategy
Check for a file specific to that strategy (eg for the uuids() strategy). Write tests for all invalid argument handling in Strategies with optional dependencies should go in hypothesis.extras, and the tests in their own module (ie not in cover). When you think you might be done, push and let our CI system point out any failing tests or non-covered code!
I've made some internal changes
That's not very specific - you should probably refer to the test-finding tips in the next section. Remember that tests/cover is reasonably quick unit-test style tests - you should consider writing more intensive integration tests too, but put them in tests/nocover with the others.

Finding particular tests

With the sheer size and variety in this directory finding a specific thing can be tricky. Tips:

  • Check for filenames that are relevant to your contribution.
  • Use git grep to search for keywords, e.g. the name of a strategy you've changed.
  • Deliberately break something related to your code, and see which tests fail.
  • Ask a maintainer! Sometimes the structure is just arbitrary, and other tactics don't work - but we want to help!

About each group of tests

Still here? Here's a note on what to expect in each directory.

Useful shared testing code, including test setup and a few helper functions in Also read up on pytest features such as mark.parametrize, mark.skipif, and raises for other functions that are often useful when writing tests.
As for cover/, but specific to hypothesis.internal.conjecture.

The home of enough tests to get 100% branch coverage, as quickly as possible without compromising on test power. This can be an intimidating target, but it's entirely achievable and the maintainers are (still) here to help.

This directory alone has around two-thirds of the tests for Hypothesis (~8k of ~12k lines of code). If you're adding or fixing tests, chances are therefore good that they're in here!

Tests which depend on the pytz or dateutil packages for timezones.
Tests for the Django extra. Includes a toy application, to give us lots of models to generate.
Tests for the Lark extra for context-free grammars, which depend on the lark-parser package.

More expensive and longer-running tests, typically used to test trickier interactions or check for regressions in expensive bugs. Lots of tests about how values shrink, databases, compatibility, etc.

New tests that are not required for full coverage of code branches or behaviour should also go in nocover, to keep cover reasonably fast.

Tests for the Numpy extra.
Tests for the Pandas extra.
Hypothesis has excellent integration with pytest, though we are careful to support other test runners including unittest and nose. This is where we test that our pytest integration is working properly.
Tests that various hard-to-find examples do in fact get found by Hypothesis, as well as some stuff about example shrinking. Mostly intended for tests of the form "Hypothesis finds an example of this condition" + assertions about which example it finds.