What tools or libraries do you use for writing tests in your projects?

In Python, the most commonly used tools and libraries for writing tests are:

• unittest — a built-in module for writing and running tests.
• pytest — a popular framework with a convenient syntax and advanced features.
• mock (unittest.mock) — for creating mock objects and stubs.
• tox — for automating testing in different environments.
• coverage.py — for measuring code coverage by tests.

The choice depends on the project, but most often, pytest is used together with mock for convenience and flexibility.