Cryptographically random isn't the aim here - pseudorandom is.
A seedable black-box RNG that guarantees what seed corresponds to what stream is way simpler to use than a list of random numbers, IMHO. It's the difference between copying one number and copying a million.
> A seedable black-box RNG that guarantees what seed corresponds
If you can control when the blackbox gets updated, or the blackbox carries a guarantee of stable output for any given seed over the while time of its existence, yes. But if you are using OS provided RNGs, as a for instance, their behaviour is not defined (well they are, but those definitions are not set in stone) and may change as kernel updates happen.
That is why I suggest "making your own simple PRNG". This could be as simple as picking a known documented algorithm as implemented by a particular library and using that in your test cases - it doesn't need to be as much as writing your own function even.
A seedable black-box RNG that guarantees what seed corresponds to what stream is way simpler to use than a list of random numbers, IMHO. It's the difference between copying one number and copying a million.