The answer to 'how to test electrical repair' is to use a multimeter to test for voltage, current, and continuity. First, turn off the power to the circuit you want to test. Then, set your multimeter to the appropriate setting for the test you want to perform. For voltage, set it to the voltage scale that matches the circuit. For current, set it to the amperage scale. And for continuity, set it to the continuity or resistance scale. Touch the probes to the circuit and read the results on the multimeter display. This will help you identify any issues with the wiring or components.
It's important to take safety precautions when testing electrical circuits, like wearing insulated gloves and working in a well-lit area. If you're not comfortable working with electricity or don't have the right tools, it's best to call a licensed electrician to diagnose and repair the issue.