The tomato test, or tomato slicing test, is a handy way to see if your knives could do with sharpening. The idea is that a properly sharpened blade should slice through the taut skin of a tomato with minimal pressure.
Somewhat counterintuitively, most cooks seem to agree that sharp knives reduce the risk of accidents as you don't have to push down as hard as with blunt knives.
To do the tomato slicing test: Place a tomato on a board and gently run the knife over the top surface. A sharp blade will glide through the tomato skin, cutting it precisely all the way down. You shouldn't need to apply any pressure if the knife has weight. If you need to push down to pierce the skin, it could be time to sharpen.
Cutting the top off the tomato first allows it to sit stably on its end, so you don't have to hold it.
Alternatively, you could use a serrated knife which is handy for foods with a hard outside and a soft inside.
The sharper the knife, the less mess you'll make and the easier you can ghost cook.
Also see the egg float test