To ensure the operational reliability of VSC-valves, operational tests must be conducted after their final design and before commissioning to validate their tolerance to critical stresses under actual operating conditions and the correctness of the design. Currently, grid-forming VSC-valves are increasingly being applied in engineering projects. However, existing test methods generally do not account for grid-forming characteristics. Therefore, to address the operational scenario where a grid-forming converter valve injects sudden reactive power during grid voltage dips, leading to current surges, this paper proposes a power step test based on a full-bridge inverter back-to-back test topology. A test platform was constructed and experiments were performed. The test results demonstrate that the proposed method can accurately replicate the power step operational scenarios of grid-forming VSC-valves.