A new test for random number generators: Schwinger-Dyson equations for   the Ising model
  We use a set of Schwinger-Dyson equations for the Ising Model to check several random number generators. For the model in two and three dimensions, it is shown that the equations are sensitive tests of bias originated by the random numbers. The method is almost costless in computer time when added to any simulation. 
H. G. Ballesteros, V. Martin-Mayor