Check continuity and insulation — that's all you need.

Yes, you can test an extension cord for shorts and ground faults with a multimeter in a few minutes. No special skills required.

Set your multimeter to resistance (ohms) or continuity mode. With the cord unplugged and no load attached, test each internal wire path:

• Hot to neutral, hot to ground, neutral to ground should all read infinite resistance (OL on most meters) if the cord is good. If you get a low resistance or a beep, you have a short or a ground fault.
• Then check each pin on the plug to the corresponding pin on the socket for a near-zero resistance (or a beep) — that confirms the wire is continuous. Breakage inside the cord gives you infinite resistance.

That’s it. If any unexpected connection shows continuity, toss the cord. If any expected path is open, same.

One caveat: a multimeter won’t catch a high-resistance fault that only shows up under load. But for dead shorts or obvious ground leakage, it works fine.