The designer should know.
The good pRNG is one which fulfills all the criteria put on it :-)
OK this was vague.
It is not simple, you might have various criteria. Mostly you want some sort of "unpredictibility", i.e. you want that from the previous (relatively short) history one could not predict the future. Then you have requirements of uniformity, of course, i.e. all possible outcomes should have the same occurence. But you can put also more complicated requirements.

Had a look at dieahard? It will give you an idea.

Jan Waclawek