Abstract: The fundamental idea of the invention consists of the construction of the test device from a stationary inner basic structure (1, 7 to 11) that juts out from the wall of the test bench and houses the drive shaft (13) for the fan to be tested, from mobile, interchangeable external housing modules (18 to 24) which can be aligned in relation to one another by means of connected optical elements (32, 33), from interchangeable fittings (41 to 44, 48) for conducting air and noise reduction, in addition to interchangeable measuring devices (38 to 40) that are connected to a modular telemetry unit for determining performance data and aerodynamic and acoustic conditions required by the fan and the fittings.