Comprehensive Guide to Pytest: Installation, Execution, Fixtures, Marks, and Parameterization

1. Pytest Overview and Installation Pytest is a Python unit‑testing framework similar to unittest but more concise and feature‑rich. Install it via pip install -U pytest and verify the version with pip show pytest ; it requires Python 3.8+.

2. Running Tests Test files must follow the test_*.py or *_test.py naming pattern, and test functions must start with test_ . Tests can be run by invoking pytest -s test_file.py , using pytest.main() in code, or by matching all tests in a directory.

3. Setup and Teardown Pytest provides ten built‑in hooks such as setup_module , teardown_module , setup_function , teardown_function , setup_class , teardown_class , and their equivalents, allowing actions before and after modules, functions, or classes.

4. Fixtures Fixtures replace traditional setup/teardown by defining reusable preconditions. They can be scoped, autouse, and parameterized. Example: @pytest.fixture def case(): print("login functionality") and used in tests as def test_one(case): ... .

5. Assertions Use the built‑in assert statement for checks. Pytest enhances assertion introspection, making failures easier to diagnose.

6. Skipping Tests Tests can be skipped with pytest.skip() (runtime) or @pytest.mark.skip / @pytest.mark.skipif (declaration). Example shows skipping after five loop iterations.

7. Marks Custom marks categorize tests, e.g., @pytest.mark.login . Run specific marks with pytest -m login , combine with logical operators, or exclude with not .

8. Parameterization Use @pytest.mark.parametrize to run a test with multiple input sets. Example evaluates arithmetic expressions: @pytest.mark.parametrize("num, result", [("10 + 10", 20), ("30 - 10", 20), ("4 * 5", 20), ("40 / 2", 20)]) def test_case(num, result): assert eval(num) == result

9. Additional Features Mentioned plugins include pytest‑rerunfailures , pytest‑HTML , pytest‑repeat , pytest‑xdist , and allure‑pytest for extended reporting, parallel execution, and retry capabilities.