Oscillating water column (OWC) devices equipped with an air turbine are the most extensively studied and possibly the most reliable wave energy converters (WEC). Self-rectifying air turbines are usually employed, being the key element of the power-take-off system. Experimental testing the air turbine in realistic operating conditions is a fundamental step in turbine and WEC development. These turbines are, by definition, operating under oscillating airflows. The present paper describes the development of a novel test-rig designed to test self-rectifying air turbines under both steady and variable unidirectional airflows, and subsequent demonstration tests performed on an axial-flow impulse turbine. A real-time hardware-in-the-loop flow controller was implemented, providing the means to not only experimentally characterise the turbine's performance under realistic wave conditions, but, as importantly, to develop new advanced turbine-generator control strategies that further increase overall efficiency and survivability. Results show that a unidirectional oscillating-flow test-rig with a calibrated fan and fast actuating valve system can adequately reproduce airflows that are characteristic of an OWC air turbine's operational regime. The hardware-in-the-loop simulator implemented in an oscillating-flow test rig appears as an innovative, integrated solution for turbine testing in realistic operating flow conditions, but in a laboratory-controlled environment at a small fraction of the costs. (C) 2019 Elsevier Ltd. All rights reserved.