Some test RNGs return constant values

[AaronFeickert]

Some RNGs in the codebase used for test purposes return constant values, which renders them unsuitable.

[AaronFeickert]

Note that it is not necessarily required that test RNGs be of high entropy (like OsRng). It is acceptable to use a deterministic PRNG for basic test purposes; however, subsequent calls to the RNG must not reinitialize such a PRNG, which results in a constant return value.