private void setValueForNBytes(byte[] input, int numberBytesToSet, byte valueToSet) {
    for (int i = 0; i < numberBytesToSet; i++) {
      input[randomIndices.get(i)] = valueToSet;
    }
  }
Tests some of the more complex functions from TestUtil.
java_src/src/test/java/com/google/crypto/tink/testing/TestUtilTest.java