Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the logic errors pattern
The wrong operator, an inverted condition, a formula the right way round but backwards.
What went wrong: lineTotal returns item.price only, so 2 items at 10 count as 10.
The fix: in lineItem.js, return item.price * item.quantity;
Remember: the file where you see the wrong answer is not always the file with the bug. Follow the function call.
The pattern behind it: logic errors.