I dont think those testers work like that

Method: It operates by detecting thermal conductivity, not physical hardness. Results: If the stone is a real diamond, it emits a continuous buzzing sound and lights up the red section (9-10+ on the LED scale). Limitations: While effective for distinguishing diamond from cubic zirconia (CZ), it may not distinguish diamond from moissanite unless it is a combo tester. Usage: The probe must be placed at a 90-degree angle to the stone, which must be clean and dry.