If electrical equipment has a current tag it is deemed to be safe.
The required frequency of testing is given in Table 4 on page 20 of AS/NZS 3760 2011
Maximum interval between tests, any new untagged or out of date tagged appliance before use in any work place:
Government legislation has been in place for a number of years encouraging employers to minimize the risk of accident by electrical fault. In order for organizations to meet the safety guidelines, all electrical workplace appliances (anything with a 2 or 3 pin plug) should be tested on a regular basis.
The Electricity Act 1997 contains a number of regulations that reinforce that obligation - Regulation 69b being particularly relevant: "Electrical Safety- (1) Works, electrical installations, fittings, electrical appliances, and associated equipment must be designed, constructed, maintained, installed and used so as to be electrically safe".
Work Safe places the duty of care on employers and employees to ensure the safety of everybody at work. They require that "as may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger".