In this paper, we have designed and developed a testbed for proof-of-concept demonstration and performance assessment of a cognitive spectrum sharing protocol based on cooperative relaying. The packet error rate (PER) for both primary and secondary systems are measured to quantify their respective performance. Spectrum access probability for the secondary system is also measured. Measurement results showed that the proposed spectrum sharing protocol is able to assist the primary system to achieve a better PER and at the same time allows spectrum access for the secondary system.