It's for so much more than cake
One of the most interesting parts of going to a culinary program is noticing how often we use certain tools. During each class I'm guaranteed to go through a dozen metal bowls and at least four side towels. We deploy a chef's knife almost every class, a paring knife only sometimes. I use my whisk a lot, but I have yet to break out my spatula, a tool I use all the time at home. But one tool I use almost every class that I didn't anticipate—I didn't even own one before the program started—is a cake tester.
A cake tester is a humble little tool, essentially a small skewer with a plastic handle. They are extremely cheap: You can buy a dozen of them for under $10 on Amazon. And they're useful for so much more than cake. Do you need to check if your fish is done? How about chicken? Potatoes? Steak? Sure, you could poke them with a paring knife or a fork to see how resistant they are, but it'll leave a big scar on your meat, particularly something as fragile as fish. A cake tester allows you to test the resistance of the meat or vegetable with a very small incision. Its handle makes it much easier to manuever than a plain metal or wooden skewer and also less likely that you'll poke the tool clear through the piece of fish.
Using the cake tester has the added advantage of training your senses to figure out when food is done cooking rather than relying on how many minutes it's been in the pan or how high the heat is up—one of those essential chef skills. So do yourself a favor and pick up one or two. You'd be surprised at how often you end up using it.