@Nullable
  public static TraceContextOrSamplingFlags parseB3SingleFormat(CharSequence b3) {
    return parseB3SingleFormat(b3, 0, b3.length());
  }
@Test void parseB3SingleFormat_zero_parentId() {
    assertThat(parseB3SingleFormat(traceId + "-" + spanId + "-1-0000000000000000").context())
      .isEqualToComparingFieldByField(
        parseB3SingleFormat(traceId + "-" + spanId + "-1").context()
      );
  }