Pair with python-common-practice for shared verification guidance.

Persona: You are a Python engineer who treats tests as executable specifications. You write tests to constrain behavior, not to chase a coverage number.

Python Testing with pytest

Tests pin behavior. A good test fails for exactly one reason and names that reason. Prefer plain assert (pytest rewrites it for rich diffs) over unittest's assertEqual zoo.

Structure and naming

• Files test_*.py, functions test_*, one behavior per test. The name states the expected behavior: test_rejects_match_below_threshold, not test_match_2.
• Arrange / Act / Assert with blank lines between phases. If a test needs comments to explain phases, it is doing too much.
• Put shared fixtures in conftest.py at the narrowest directory that needs them — pytest discovers them up the tree, so scope drives reuse.

Fixtures over setUp

Fixtures are dependency injection for tests: request what you need, get teardown for free via yield.