@Override public String toString() {
    boolean traceHi = traceIdHigh != 0;
    char[] result = new char[((traceHi ? 3 : 2) * 16) + 1]; // 2 ids and the delimiter
    int pos = 0;
    if (traceHi) {
      writeHexLong(result, pos, traceIdHigh);
      pos += 16;
    }
    writeHexLong(result, pos, traceId);
    pos += 16;
    result[pos++] = '/';
    writeHexLong(result, pos, spanId);
    return new String(result);
  }
@Test void testToString() {
    TraceContext context =
      TraceContext.newBuilder().traceIdHigh(333L).traceId(444L).spanId(3).parentId(2L).build();

    assertThat(context.toString())
      .isEqualTo("000000000000014d00000000000001bc/0000000000000003");
  }