Electrical equipment must be checked by way of periodic electrical testing in order to spot early signs of deterioration or damage. Electrical equipment should be tested more thoroughly by competent PAT testers often enough so that there is very little chance that the electrical equipment will become potentially dangerous between electrical testing. Electrical equipment used in a harsher environment should be tested much more frequently.
It is considered good practice to take note of how frequently equipment used for work needs be tested, note your findings, make sure the periodic electrical testing is carried out, and keep a note of results of the tests.