 Proof tests may be performed before a new design or unit is allowed to enter service, or perform additional uses, or to verify that an existing unit is still functional as intended.Cranes and derricks are proof tested when called on for potentially dangerous load levels or high-valued cargoes.Similarly, items which are smaller and more common (rope and cable, slings, shackles and eyes) are nevertheless in the load path and a failure risk if not tested.