If you're not sure whether your gravy has gone bad, there are a few things you can do to test it. First, take a look at the color and texture of the gravy. If it's significantly darker or lighter than when you made it, or if it has chunks in it that weren't there before, those are signs that it's gone bad. Another way to tell is by smell: if your gravy smells sour or rancid, throw it out. Finally, give the gravy a taste: if it tastes off in any way, don't risk eating it.
In general, gravy only lasts for a few days in the fridge, so if you're not sure whether yours is still good, err on the side of caution and toss it out. With that said, there are a few ways you can extend its shelf life. One is to store the gravy in an airtight container; this will prevent bacteria from getting into it and spoiling it prematurely. Another is to freeze the gravy; this will keep it fresh for several months.
So there you have it: how to tell if your gravy has gone bad, and what you can do to prolong its lifespan. Now get out there and enjoy all those holiday feasts!