Engineering Craft › Testing

Test Case and Test Suite

A single scenario being checked, and a group of them run together.

Also known as: test case, test suite, test cases

A test case is a single scenario being checked: one situation, one expected outcome. A test suite is a group of test cases run together.

# test_cart.py: a suite of related cases
def test_empty_cart_total_is_zero():            # test case
    assert Cart().total() == 0

def test_adding_an_item_increases_total():      # test case
    cart = Cart()
    cart.add(Item(price=10))
    assert cart.total() == 10

def test_negative_quantity_is_rejected():       # test case
    with pytest.raises(ValueError):
        Cart().add(Item(price=10), qty=-1)

Each case has a clear name that states the situation and the expectation, and a pass or fail result.

How suites are organized

Suites usually mirror the code: a file or class per module, folders per area, plus separate groups by kind (unit, integration, end-to-end) or speed (a fast “smoke” suite and a slower “full” one) (smoke tests).

pytest                          # run everything
pytest tests/test_cart.py       # one file
pytest -k "negative"            # cases whose name matches

(test runners)

Writing good cases

• One scenario per case, so a failure points to one problem.
• A descriptive name: test_expired_coupon_is_rejected tells you what broke without reading the code.
• Independent: no case relies on another having run first (test isolation).
• Cover edges: empty, one, many, invalid, boundary.
• Share setup with fixtures, not copy-paste (test fixtures).

Keeping a suite healthy

• Run it often, in CI, and keep it fast.
• Fix or remove flaky cases.
• Delete obsolete ones.
• Treat test code like production code: readable and maintained.