Tests should fail for exactly one reason - aim for a single assert per test
Python clean test tip:
Aim for a single assert per test. Tests will be more readable and it's easier to locate a defect when a test is failing.
import pytest class User: def __init__(self, username): if len(username) < 1: raise Exception("Username must not be empty.") self._username = username @property def username(self): return self._username # BAD def test_user(): username = "johndoe" assert User(username).username == username username = "" with pytest.raises(Exception): User(username) # GOOD def test_user_with_valid_username_can_be_initialized(): username = "johndoe" assert User(username).username == username def test_user_with_empty_username_cannot_be_initialized(): username = "" with pytest.raises(Exception): User(username)
It's fine to deviate from this, to include multiple asserts per test as long as you're testing the same concept.