A method of testing and/or controlling the operation of an axial turbomachine through which passes a gas stream, includes the following actions: measurement of operating parameters of the turbomachine, said parameters including pressure in the gas stream at different axial positions, and calculation of operating conditions of the turbomachine from the measured parameters and the Laplace coefficient γ of the gas passing through the turbomachine, wherein the measurement of parameters includes a measurement of the temperature of the gas stream, and the calculation of operating conditions includes a determination of the Laplace coefficient γ on the basis of the measurement of the temperature of the gas stream.