A method of fault diagnosis during testing of a turbine unit includes a) obtaining measurement data from turbine sensors and testing sensors, b) calculating at least one parameter value based on measurement data, c) determining a deviation of the measurement data and the at least one parameter value by comparing the measurement data and the at least one parameter value with predetermined reference data, and d) matching the determined deviation to a plurality of predetermined fault signatures in order to detect a fault. The plurality of predetermined fault signatures includes a first set of fault signatures and a second set of fault signatures, the first set of fault signatures corresponding to turbine sensor faults and/or testing sensor faults and assumed fault-free turbine components, the second set of fault signatures corresponding to turbine component faults and assumed fault-free turbine sensors and testing sensors.