@Nullable
  public static TraceContextOrSamplingFlags parseB3SingleFormat(CharSequence b3) {
    return parseB3SingleFormat(b3, 0, b3.length());
  }
@Test void parseB3SingleFormat_spanIdsNotYetSampled128() {
    assertThat(parseB3SingleFormat(traceIdHigh + traceId + "-" + spanId).context())
      .isEqualToComparingFieldByField(TraceContext.newBuilder()
        .traceIdHigh(Long.parseUnsignedLong(traceIdHigh, 16))
        .traceId(Long.parseUnsignedLong(traceId, 16))
        .spanId(Long.parseUnsignedLong(spanId, 16)).build()
      );
  }