@Nullable
  public static TraceContextOrSamplingFlags parseB3SingleFormat(CharSequence b3) {
    return parseB3SingleFormat(b3, 0, b3.length());
  }
@Test void parseB3SingleFormat_sampled() {
    assertThat(parseB3SingleFormat("1"))
      .isEqualTo(TraceContextOrSamplingFlags.SAMPLED);
  }