A receptacle tester or outlet tester is a evice used to verify that an AC wall outlet is wired properly. The tester itself is small device which looks like the "plug in" end of a power cord, with several lights on it rather than an attached cord. Although a multimeter could be used to perform a series of tests which would give the same results, an outlet tester can perform the entire array of tests by simply plugging the device into the outlet once and observing the state of the lights. The tester performs several tests at once but the tests themselves essentially fall into two categories: tests which determine that the outlet actually functions and tests which determine that the outlet is properly wired for safe operation.