Statistical tests for PRNG that generates a sequence which is not binary Is there a pratical application to PRNG that generates a sequence which is not a binary one? A ternary, quaternary sequence, for instance. If so, how can we test this? Is there any alternative test suite, like NIST test suite in order to test the randomness for non-binary sequences? For example, what if I generate a sequence in modulo 255 and then use it to encrypt an image in one-time pad manner via adding the values of pixels by the generated sequence in modulo 255 ?
Randomness testing uses asymptotic properties. Thus, as the length of your input increases the effect you are concerned about will disappear. 

Specifically, there is no need to convert ternary $1$ or $2-$tuples to binary. If you let $n$ increase you cover the interval $\{0,1,\ldots,3^n-1\}$ and then you convert these integers to binary, paying at most a 1 trit (Shannon's term for entropy in base 3) penalty in entropy. Since a decent ternary source should yield not much less than $$\left(\frac{\log 3}{\log 2}\right)n$$ bits or $n$ trits of entropy, there is nothing to worry about.