An arc fault detection circuit for an arc fault circuit interrupter (AFCI). The arc fault detection circuit includes an arc detecting circuit for detecting an arc fault in one or more power supply lines and outputting a detected signal, an arc filtering circuit electrically coupled to an output terminal of the arc detecting circuit for removing signal parts unrelated to the arc fault from the detected signal and outputting a filtered half-cycle signal, and an arc processing circuit electrically coupled to an output terminal of the arc filtering circuit for generating, based on the filtered half-cycle signal received, a processed half-cycle signal characterizing the arc fault. The arc fault detection circuit also includes simulated arc testing circuit that has a user-touchable test switch, and an arc oscillator to generate a simulated arc fault signal for testing the arc fault detection circuit or its respective components.