pytest

Pytest is a mature Python testing framework used to write simple unit tests and complex functional tests. It emphasizes readable test code and provides powerful features while remaining easy to use. Pytest originated as py.test, created by Holger Krekel, and later adopted the pytest name as the project matured. It is one of the most widely used testing tools in the Python ecosystem.

Key features include a powerful assertion introspection that shows details in failures, a rich fixture system for setup and modular test components, and support for parametrized testing to run the same test with different data. Tests are discovered automatically by name convention, without requiring classes or boilerplate, though class-based tests are supported. Pytest supports markers to categorize tests and to customize behavior. It also integrates with unittest-style tests and can run with numerous plugins for coverage, mocking, and specialized frameworks like Django or Flask applications.

Usage: Install via pip, then run pytest from the project root to discover and execute tests. Tests are typically written as functions named test_..., using plain Python assert statements. Fixtures are defined with the fixture decorator and can be composed and scoped (function, module, session). Parametrization is done with the parametrize decorator to create multiple test cases from a single test function.

Plugin architecture and ecosystem: Pytest provides a robust plugin architecture; thousands of plugins extend reporting, coverage, parallel execution, and integrations with CI systems. It has a large ecosystem of community contributions and is widely used in continuous integration workflows.