Ground testing campaign conducted on the FLEXOP demonstrator aircraft is presented in this paper. The conducted tests are grouped in structural, flight system and integration tests. Along with the description of the test setup and test execution, the main findings and conclusions are also given. The structural tests comprise the static, ground vibration and the airworthiness test. The static and the ground vibration tests were used for structural characterisation of the manufactured wings and airframe as a whole. Assessment and calibration of the Fibre Brag strain sensing system for wing shape and load reconstruction is also presented within this context. The airworthiness test is used to demonstrate the structural integrity of the manufactured wings under specified limit loads. Within the context of the flight system tests, the main components of the on-board autopilot hardware-software system are briefly introduced including the signal data flow from the RC transmitter to the aircraft controls, the functionality of the baseline autopilot software and the communication with the ground station. All of these components are integrated into the hardware-in-the-loop environment, which is also briefly introduced along with the servo motor identification and the hardware delay measurements. The measured hardware delay was considered in the design of the baseline and flutter controllers. The flutter controllers were tested together with the baseline controller in the software-in-the-loop environment. System integration tests are presented last. In this context the airbrake, the engine, the compatibility of electronic components, the range and the taxi tests are presented. @en