For example, suppose you want to write a test for the shipOrder(orderId) function, and you want it to depend on the test for the placeOrder(shoppingCart) -> OrderId function. Even if you are fine calling placeOrder twice, once for the placeOrder test and once for the placeOrderAndShipOrder test, you still need the placeOrder test to provide an order ID to the second test, and not just a confirmation that it completed successfully.