pytest: tests that are actually pleasant to write

Python's stdlib has unittest, but nobody uses it if pytest is an option. pytest is:

• Zero ceremony — a function named test_* in a file named test_*.py is a test.
• Plain assert — no self.assertEqual verbosity.
• Rich failure output — shows the actual value that broke.

The whole API

• assert expected == actual — pytest rewrites this to show both sides on failure.
• with pytest.raises(SomeError, match="..."): — assert exception + optional message.
• @pytest.mark.parametrize("a,b,expected", [...]) — one test, many inputs.
• @pytest.fixture — reusable setup (next lesson).
• pytest -v verbose, pytest -k slugify filter by name, pytest -x stop on first failure.

Test organization

myapp/
  __init__.py
  slugify.py
tests/
  test_slugify.py

Then just run pytest. It discovers everything.

Coverage

pip install pytest-cov
pytest --cov=myapp --cov-report=term-missing

Shows which lines your tests miss. Aim for 80%+ on business logic; don't chase 100% on plumbing.

Try it

1. Add a test that slugify("Python 🐍") behaves how you'd want.
2. Add a parametrize case where b is negative.