How do you test for earth in a lighting circuit?

To test for earth in a lighting circuit, you can use a multimeter set to measure resistance or continuity. First, ensure the circuit is turned off and isolate the lighting circuit from the power supply. Then, connect one probe of the multimeter to the earth terminal and the other probe to a known earth point, such as a metal part of the fixture or an earth rod. A low resistance reading indicates a good earth connection, while a high or infinite reading suggests a problem with the earthing.