How to test existing ethernet cable outlets?
Your testing method seems reasonable and probably rules out continuity between those two drops. (The exception might be if your router or switch don't have Auto MDI-X sensing and you needed a crossover cable, but that's unlikely as most devices made in the past few years should figure that out automatically.)

So if these two drops aren't directly linked, where do they go? Most often these run to a basement, attic, or closet. Possibly (but not necessarily) wherever your home's telephone wiring terminates. As a first step, try to figure out where the lines go - perhaps you can find a common termination point and locate your router or switch there to supply the drops.

If visual inspection isn't working, you can use a tool called a wire tracer or tone-and-probe kit to track where the cables go in your walls. The tool has two pieces: a tone generator and a probe. You'll either plug the tone generator into an RJ45 port, or open up the drop and clip the tone generator to a wire in the ethernet cable. The toner generates a signal that flows through the cable, effectively using the cable as a radio broadcast antenna. The probe then picks up on this signal (usually a beep or siren type tone) and replays it. You can move the probe back and forth along your walls, and identify the path the cable is taking.



Tone and probe kits are not super cheap tools, but a basic comms-oriented one can be had online for around $25 (example). I have a cheap Harbor Freight one that I've gotten a surprising amount of use from in various wiring projects.