Arrange, act and assert

How to do it

Separate the three parts with a blank line. Do only one action per test. Keep the setup short by using helpers or factories. If a test needs many actions, it is probably a flow that belongs in an integration test.

Example

def test_cancelled_order_releases_stock():
    stock = Stock(sku="MUG-1", count=3)
    order = place_order(stock, quantity=2)

    order.cancel()

    assert stock.count == 3

test('a cancelled order releases its stock', () => {
  const stock = new Stock('MUG-1', 3);
  const order = placeOrder(stock, 2);

  order.cancel();

  expect(stock.count).toBe(3);
});

How to check

Pick ten tests at random. Each has setup, then one call to the code under test, then only assertions. No call to the code under test follows an assertion.