I don't think that unit testing randomness can *properly* fit in a single test.. on the other hand, by not having a test like this there is no way to guarantee that we generate random characters.

Armed with this test, we can make sure that the generated sequence meets our needs, even if this is not *objectively* random. This technique is adapted from the excellent [Unit Testing Randomness](http://c2.com/cgi/wiki?UnitTestingRandomness) wiki page :)