@Test public void should_add_parent_trace_when_context_injected_on_headers() {

  ProducerRecord<Object, String> record = new ProducerRecord<>(TEST_TOPIC, TEST_KEY, TEST_VALUE);
  tracingProducer.injector.inject(parent, new KafkaProducerRequest(record));
  tracingProducer.send(record);
  mockProducer.completeNext();
  MutableSpan producerSpan = spans.get(0);
  assertThat(producerSpan.kind()).isEqualTo(PRODUCER);
  assertChildOf(producerSpan, parent);
  assertThat(lastHeaders(mockProducer))
    .containsEntry("b3", producerSpan.traceId() + "-" + producerSpan.id() + "-1");
}