A hash function should not be reading outside the bounds of the key (causing UB).

Flipping a bit of a key should, with overwhelmingly high probability, result in a different hash.

Hashing the same key twice should always produce the same result.

The memory alignment of the key should not affect the hash result.

Appending zero bytes to a key should always cause it to produce a different hash value (AppendedZeroesTest). (Security relevant)