When buying eggs, be sure to check the date of manufacture. If the eggs are unlabeled, try shaking them slightly. The contents should not hang out like something liquid.
The remaining methods are suitable for testing at home.
Put it in a container with cold water. A very fresh egg will remain at the bottom and at the same time will lie sideways.
If the egg is on the narrow end, it can also be eaten, but it is better as soon as possible. By the way, such an egg shell will be better to move away from the protein without sticking to it, unlike fresh.
An egg that has surfaced should not be eaten. The fact is that the older it is, the more porous the shell becomes. Due to the accumulated air, the egg floats up.
Break and inspect the shell: if there are black or brown spots on it, these are traces of mold.
The fresh yolk is smooth and rounded. The protein seems to be divided into two parts: a thicker one next to the yolk and a thinner one at the edges. The older the egg, the worse the protein will hold its shape.
The egg itself should not exude an unpleasant pungent smell — you definitely can't eat that. Fresh yolks and whites have little or no smell.