### Question:
FilterIdGenerator { public String nextId() { final byte[] randomBytes = new byte[16]; secureRandom.nextBytes(randomBytes); return Quantity.create(randomBytes); }  String nextId();  }### Answer:
@Test public void idIsAHexString() { final FilterIdGenerator generator = new FilterIdGenerator(); final String s = generator.nextId(); final UInt256 bytes = UInt256.fromHexString(s); assertThat(bytes.toShortHexString()).isEqualTo(s); }