As integrated circuits have become more complex, testing them has become more challenging. Tests are required in three situations. The earliest test is applied at the wafer stage of fabrication to ascertain that the manufacturing process has succeeded and that packaging of the individual integrated circuits, one of the most expensive stages of manufacture, is worthwhile. The second phase is when the integrated circuit has been incorporated into an electronic product. This test, which is often applied at the board stage, when the printed-circuit card is tested, also checks for faults in the board and in its assembly. The final test situation is when the circuit is in operation, to check whether a fault has occurred and to indicate to the user that the system is functioning correctly.