@Test public void injectKindFormat() {

  B3Propagation.Factory factory = (B3Propagation.Factory) B3Propagation.newFactoryBuilder()
    .injectFormat(Span.Kind.CLIENT, Format.SINGLE)
    .build();
  assertThat(factory.injectorFactory).extracting("clientInjectorFunction")
    .isEqualTo(Format.SINGLE);
}