Python unittest Skill
Core Patterns
Basic Test
import unittest
class TestCalculator(unittest.TestCase):
def setUp(self):
self.calc = Calculator()
def test_add(self):
self.assertEqual(self.calc.add(2, 3), 5)
def test_divide_by_zero(self):
with self.assertRaises(ZeroDivisionError):
self.calc.divide(10, 0)
def test_multiple_assertions(self):
self.assertEqual(self.calc.add(2, 2), 4)
self.assertEqual(self.calc.subtract(5, 3), 2)
self.assertAlmostEqual(self.calc.divide(10, 3), 3.333, places=3)
def tearDown(self):
pass # cleanup
if __name__ == '__main__':
unittest.main()Assertions
self.assertEqual(a, b)
self.assertNotEqual(a, b)
self.assertTrue(condition)
self.assertFalse(condition)
self.assertIsNone(obj)
self.assertIsNotNone(obj)
self.assertIs(a, b) # same object
self.assertIn(item, collection)
self.assertNotIn(item, collection)
self.assertIsInstance(obj, cls)
self.assertAlmostEqual(a, b, places=5)
self.assertGreater(a, b)
self.assertLess(a, b)
self.assertRegex(str, r'\d+')
self.assertCountEqual(a, b) # same elements, any order
# Exception
with self.assertRaises(ValueError) as ctx:
raise ValueError("bad")
self.assertIn("bad", str(ctx.exception))
# Warning
with self.assertWarns(DeprecationWarning):
deprecated_function()SubTest (Parameterized)
def test_add_multiple(self):
test_cases = [(2, 3, 5), (-1, 1, 0), (0, 0, 0)]
for a, b, expected in test_cases:
with self.subTest(a=a, b=b):
self.assertEqual(self.calc.add(a, b), expected)Mocking
from unittest.mock import patch, MagicMock, Mock
class TestUserService(unittest.TestCase):
@patch('myapp.service.UserRepository')
@patch('myapp.service.EmailService')
def test_create_user(self, MockEmail, MockRepo):
mock_repo = MockRepo.return_value
mock_repo.save.return_value = User(1, 'Alice')
service = UserService()
result = service.create_user('alice@test.com', 'Alice')
self.assertEqual(result.id, 1)
mock_repo.save.assert_called_once()
MockEmail.return_value.send_welcome.assert_called_with('alice@test.com')Lifecycle
setUpClass() → Once before all tests (classmethod)
setUp() → Before each test
test_method() → Test
tearDown() → After each test
tearDownClass() → Once after all tests (classmethod)Run: python -m unittest or python -m unittest test_module.TestClass.test_method
Discover: python -m unittest discover -s tests -p "test_*.py"
Deep Patterns
For advanced patterns, debugging guides, CI/CD integration, and best practices, see reference/playbook.md.