Generate a bunch of passwords and check the frequency for each one. Since you (presumably) know how may words there are and you know the number of digits in the number, you ought be able to set a sensible theoretical threshold for the likelihood of generating duplicates of passwords (or password parts if you want to deal on that level).

If you want to work a little harder you could look at letter frequency in the word set and letter frequency in the generated test set and check that they are similar.