In the last decades, small satellites have played an important role in space missions. Due to their reduced dimension and costs, they became affordable to smaller companies and research laboratories to conduct scientific experiments and technological demonstrations in space. In addition, the number of these satellites has considerably increased due to their wide use in technological, scientific and commercial domains. In this scenario, autonomous architectures, as well as miniaturized mechanical subsystems for small satellites, are continuously investigated. Experimental Rendezvous in Microgravity Environment Study (ERMES) is a student project that focuses on the simulation of an autonomous docking manoeuvres between two CubeSats mock-ups equipped with miniaturized Guidance Navigation and Control systems and mechanical docking interfaces. ERMES aims to integrate different subsystems for autonomous docking, to increase the Technology Readiness Level and to study possible applications for in-orbit servicing. This paper deals with the design and development of the tests for autonomous docking manoeuvres between two CubeSats mock-ups to be performed in a reduced-gravity environment during a parabolic flight. A Target-Chaser configuration has been selected, where the Chaser is fully active and the Target is cooperative. The Chaser is equipped with a miniaturized cold gas propulsion system with eight thrusters to control its attitude and position; in contrast, the Target has a set of three reaction wheels to control only its attitude. The tested miniaturized mechanical docking interfaces employs a probe-drogue configuration. The most demanding aspect of the development phase will be the dedicated software for the proximity navigation. The reduced-gravity conditions will be achieved during a campaign of parabolic flights thanks to the participation to the European Space Agency “Fly Your Thesis!” programme 2022.