With the power shut off, connect a test wire to a circuit wire in one box. Run the test wire to the other box. Clip the lead ...

so there is no need for a power switch. [David] reckons the CR927 button cell ought to last pretty long. For those interested in building this handy tester, [David] has shared the Eagle CAD files ...

Easily and accurately measure dynamic characteristics on a Wide-Bandgap power semiconductor bare chip without soldering or probe needles ... parasitics in the test circuit and produces clean ...