@Override
          public int read(byte[] b, int off, int len) {
            if (numReads == 0) {
              return -1;
            }
            --numReads;
            b[off] = randomness;
            return 1;
          }
Tests for Tink internal Util class.
java_src/src/test/java/com/google/crypto/tink/internal/UtilTest.java