public static BaggageField create(String name) {
    return new BaggageField(name, ExtraBaggageContext.get());
  }
@Test void internalStorage() {
    assertThat(BaggageField.create("foo").context)
      .isSameAs(ExtraBaggageContext.get());

    BaggageContext context = mock(BaggageContext.class);
    assertThat(new BaggageField("context", context).context)
      .isSameAs(context);
  }