Testing involves a combination of electrical, thermal, and mechanical assessments. Electrical tests include insulation resistance measurements, turns ratio tests, and dielectric tests to verify the integrity of windings and insulation. Thermal imaging detects hotspots indicating overheating. Oil analysis identifies contaminants or degradation products. Mechanical tests examine structural components for wear or damage. These tests are performed during commissioning, routine maintenance, and after any significant events to ensure the transformer remains reliable and safe for operation.