A method for testing a radar level gauge arranged at a tank containing a product, said radar level gauge comprising a reference reflector at or above a high level alarm limit for said tank, the reference reflector being arranged at a known reference reflector level (L RR), wherein the method comprises the steps of: transmitting a plurality of electromagnetic transmit signals (S T) towards a surface of said product in the tank; receiving a plurality of electromagnetic reflection signals, each including several echoes resulting from reflection of a corresponding one of said electromagnetic transmit signals (S T) at impedance discontinuities encountered by the electromagnetic transmit signal; determining a first verification level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals (S T) at said reference reflector; determining a second verification level based on a surface echo resulting from reflection of one of said electromagnetic transmit signals (S T) at said surface of the product; and determining a test result based on a relation between said first verification level and said known reference reflector level (L RR), and on said second verification level, characterized in that: said radar level gauge is further controllable to operate in a filling level measuring state or a system proof test state, said method further comprising the steps of: determining in said radar level gauge a filling level of said product based on said surface echo; providing from said radar level gauge a signal indicative of said filling level to a host system; receiving, as an input to said radar level gauge, a system proof test start command; controlling, in response to said system proof test start command, said radar level gauge to enter said proof test state, said system proof test state meaning a high level alarm test state; determining a proof test filling level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals (S T) at the reference reflector; providing, to said host system, a signal indicative of the proof test filling level; monitoring a reaction of said host system to the signal indicating the filling level at or above the high level alarm limit; and controlling said radar level gauge to exit said system proof test state. transmitting a plurality of electromagnetic transmit signals (S T) towards a surface of said product in the tank; receiving a plurality of electromagnetic reflection signals, each including several echoes resulting from reflection of a corresponding one of said electromagnetic transmit signals (S T) at impedance discontinuities encountered by the electromagnetic transmit signal; determining a first verification level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals (S T) at said reference reflector; determining a second verification level based on a surface echo resulting from reflection of one of said electromagnetic transmit signals (S T) at said surface of the product; and determining a test result based on a relation between said first verification level and said known reference reflector level (L RR), and on said second verification level, characterized in that: said radar level gauge is further controllable to operate in a filling level measuring state or a system proof test state, said method further comprising the steps of: determining in said radar level gauge a filling level of said product based on said surface echo; providing from said radar level gauge a signal indicative of said filling level to a host system; receiving, as an input to said radar level gauge, a system proof test start command; controlling, in response to said system proof test start command, said radar level gauge to enter said proof test state, said system proof test state meaning a high level alarm test state; determining a proof test filling level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals (S T) at the reference reflector; providing, to said host system, a signal indicative of the proof test filling level; monitoring a reaction of said host system to the signal indicating the filling level at or above the high level alarm limit; and controlling said radar level gauge to exit said system proof test state. determining in said radar level gauge a filling level of said product based on said surface echo; providing from said radar level gauge a signal indicative of said filling level to a host system; receiving, as an input to said radar level gauge, a system proof test start command; controlling, in response to said system proof test start command, said radar level gauge to enter said proof test state, said system proof test state meaning a high level alarm test state; determining a proof test filling level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals (S T) at the reference reflector; providing, to said host system, a signal indicative of the proof test filling level; monitoring a reaction of said host system to the signal indicating the filling level at or above the high level alarm limit; and controlling said radar level gauge to exit said system proof test state.