PyHamcrest is a framework for writing matcher objects, allowing you to
declaratively define "match" rules. There are a number of situations where
matchers are invaluable, such as UI validation, or data filtering, but it is in
the area of writing flexible tests that matchers are most commonly used.

When writing tests it is sometimes difficult to get the balance right between
overspecifying the test (and making it brittle to changes), and not specifying
enough (making the test less valuable since it continues to pass even when the
thing being tested is broken). Having a tool that allows you to pick out
precisely the aspect under test and describe the values it should have, to a
controlled level of precision, helps greatly in writing tests that are "just
right." Such tests fail when the behavior of the aspect under test deviates
from the expected behavior, yet continue to pass when minor, unrelated changes
to the behaviour are made.

Homepage:
https://github.com/hamcrest/PyHamcrest
