Cal. Pub. Util. Code § 772

Any consumer or user of any product, commodity, or service of a public utility may have any appliance used in the measurement thereof tested upon paying the fees fixed by the commission. The commission shall establish and fix reasonable fees to be paid for testing such appliances on the request of the consumer or user. The fee shall be paid by the consumer or user at the time of his request, but if the appliance is found defective or incorrect to the disadvantage of the consumer or user, the fee shall be paid by the public utility and repaid to the consumer or user under such rules as the commission prescribes.