Alternatives to testing coax cable

Several years ago, I wired coax cable connections to the main unit of my house and the basement apartment. The cable company ran two cables from an alley pole to the entry point on the house and I took it from there. Inside the house on the other side from where the outside box is to which the alley cables go is a receptacle box in which the inside two cables are connected to what is outside.

Since no one lives in the basement, I didn't get an extra service. The main unit service works fine going through all the same checkpoints (receptacle boxes and entry points). Since I am getting ready to finish the basement, I wanted to test that the basement connection from the inside receptacle still works and that some 30' of cable that runs from the entry point to the basement media box still works, particularly that it hasn't been cut by accident or rodents chewing, before I seal it with drywall.

So I disconnected the main unit connection to the active cable coming in (vs. the one that will be activated once someone actually lives there). However, the modem on the other end of that cable (basement) could not connect. The modem does connect when I take it upstairs and connect it directly to the splitter. When I did this first, several years ago, I performed the same test and it worked. Now it doesn't. It's as though the cable has been cut off somewhere on the way.

Are there alternative ways to test two ends of a coax cable? Like running some current through. I have an organic intolerance for visible wire/cable so I did a lot of remodeling just to hide it, which means my cable is buried behind the wall — while aesthetically appealing, it makes it a hell of a lot harder to troubleshoot and repair. I am trying to make darn sure the cable is cut before I tear down drywall and reinstall.