I'm not in the cryptography or random space beyond using libraries, but these visualizations are very clever. It's easy to see major problems.
edit: It shows small-periods but otherwise it's not all that useful (see below).
edit: It shows small-periods but otherwise it's not all that useful (see below).
The random number generator here is used quite often in projects and it looks pretty random. But if you look at the code you can see that it has four numbers that store state and its output can be entirely predicted from those four numbers that are consecutive outputs of the RNG.