The potential of vertical-axis wind turbines (VAWTs) for specific applications (floating off-shore or urban installations) has been reconsidered in recent years. This renewed interest has led to an increasing number of experimental studies on VAWTs. A challenge of experimental work is correctly interpreting experimental results but just as important is the design of the experimental setup. The objective of the present study is to elaborate on the complete development process of a VAWT wind tunnel test setup, from design to aerodynamic interpretation. The effect of the design choices and structural characteristics of the setup can be traced in the measured torque. The influence of structural dynamics of an experimental setup are proven to influence unsteady measurements significantly through the analysis of the spectral content of the measured torque. An extensive modal analysis of the VAWT rotor allows to link modal vibrations to their contaminating effect on the measured torque. In addition, the dynamics of the sensors and setup are found to be important contributions to the contamination of dynamic measurements. To interpret unsteady torque measurements, the complete experimental setup needs to be dynamically characterised.