pytest is the Python testing framework known for concise syntax and a powerful fixture system.
Pytest grew out of the PyPy project and was designed partly to address frustrations with Python’s built-in unittest style. Instead of requiring test classes and verbose assertion methods, pytest lets developers commonly write plain test functions using Python’s assert statement. Its assertion rewriting adds detailed information when a comparison fails.
Fixtures are one of pytest’s defining features. A fixture is a reusable function that prepares context or test data and supplies it to a test through a parameter. Fixtures can handle setup and cleanup, be shared through conftest.py files, and use function, class, module, or session scopes. Parametrization also allows one test function to run against multiple input sets.
The alternatives are not identical competitors in meaning: doctest checks examples embedded in documentation, unittest is Python’s standard-library framework, and nose was a separate third-party testing framework. Pytest can also run many unittest-style tests, making migration easier.