@Test public void should_inject_child_context() {

  try (Scope scope = currentTraceContext.newScope(parent)) {
    tracingProducer.send(new ProducerRecord<>(TEST_TOPIC, TEST_KEY, TEST_VALUE));
    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");
}