The well-known crack of a rifle, whose ball came skipping along the placid surface of the strait, and a shrill yell from the island, interrupted his speech, and announced that their passage was discovered.
An arc fault circuit interrupter (AFCI) is a circuit breaker that breaks the circuit when it detects an electric arc in the circuit it protects to prevent electrical fires. An AFCI selectively distinguishes between a harmless arc (incidental to normal operation of switches, plugs, and brushed motors), and a potentially dangerous arc (that can occur, for example, in a lamp cord which has a broken conductor).
The TEST button is designed to test the function of the electronics of the AFCI to ensure that the detection circuitry is working properly, which, in turn, triggers the mechanical operation of the device. A successful trip verifies that the device is continuing to monitor the entire branch circuit for arcing conditions.