What is Python's unittest module?

Python's built-in unittest module provides a test framework. Tests extend unittest.TestCase and define test methods starting with test_. Setup/teardown: setUp() runs before each test, tearDown() after. Class-level: setUpClass(cls) / tearDownClass(cls). Assertions: assertEqual(a, b), assertNotEqual(), assertTrue(), assertFalse(), assertIsNone(), assertIn(item, container), assertRaises(Exception, callable, *args). Run: python -m unittest discover or python -m unittest test_module. Mocking: from unittest.mock import Mock, patch, MagicMock; @patch("module.ClassName") def test(mock_class): .... Modern alternative: pytest — simpler syntax (plain functions, not classes), more powerful fixtures, rich plugin ecosystem, and better output. Most Python projects prefer pytest.