Embodiments include methods and apparatus for testing an electrical system (e.g., of an electric vehicle) that includes a high voltage (HV) energy storage system, HV contactors, one or more energy consuming components, one or more energy supplying components, an HV bus, discharge circuitry, and a control system. The control system is adapted to perform a method that includes performing a first diagnostic test to test the functionality of the HV contactors, and performing a second diagnostic test to test the functionality of the discharge circuitry. When the first and second tests have passed, the control system allows the HV contactors to be closed to enable an exchange of energy between the HV energy storage system, the one or more energy consuming components, and the one or more energy supplying components.