public static String newTraceId() {
    byte[] traceId = new byte[32];
    WriteBuffer buffer = WriteBuffer.wrap(traceId);
    buffer.writeLongHex(ThreadLocalRandom.current().nextLong());
    buffer.writeLongHex(ThreadLocalRandom.current().nextLong());
    return new String(traceId, UTF_8);
  }
Zipkin trace ids are random 64bit numbers. This creates a relatively large input to avoid
flaking out due to PRNG nuance.
zipkin-tests/src/main/java/zipkin2/TestObjects.java