private byte[] checkDecoding(String s) {
    try {
      return Base32String.decode(s);
    } catch (DecodingException e) {
      return null; // decoding failed.
    }
  }
Base32String implementation is not the same as that of RFC 4648, it drops
the last incomplete chunk and thus accepts encoded strings that should have
been rejected; also this results in multiple encoded strings being decoded
to the same byte array.
This test will catch any changes made regarding this behavior.
javatests/com/google/android/apps/authenticator/util/Base32StringTest.java