@Nullable
  public static TraceContextOrSamplingFlags parseB3SingleFormat(CharSequence b3) {
    return parseB3SingleFormat(b3, 0, b3.length());
  }
@Test void parseB3SingleFormat_parent_debug() {
    assertThat(parseB3SingleFormat(traceId + "-" + spanId + "-d-" + parentId).context())
      .isEqualToComparingFieldByField(TraceContext.newBuilder()
        .traceId(Long.parseUnsignedLong(traceId, 16))
        .parentId(Long.parseUnsignedLong(parentId, 16))
        .spanId(Long.parseUnsignedLong(spanId, 16))
        .debug(true).build()
      );
  }