Broad statistical tests are good enough for most all non-crypto RNGs - once you pass DieHarder you're probably good enough for practially all common RNG uses.

Breaking crypto RNGs is a subtle enough art that having a standardized set of tests wouldn't actually prove anything useful - it would be like saying "We tried every key in our collection on this new padlock and none of them worked, therefore the padlock is secure."

-Austin, author of SMHasher

http://random.mat.sbg.ac.at/tests/ "On this page, you will find information on tests for uniform random number generators (RNGs)"

Lossless compression algorithms. True randomness should yield near 0% compression ratios.

PractRand is a useful test suite.