@Test public void send_should_tag_topic_and_key() {

  tracingProducer.send(new ProducerRecord<>(TEST_TOPIC, TEST_KEY, TEST_VALUE));
  mockProducer.completeNext();
  MutableSpan producerSpan = spans.get(0);
  assertThat(producerSpan.kind()).isEqualTo(PRODUCER);
  assertThat(producerSpan.tags())
    .containsOnly(entry("kafka.topic", TEST_TOPIC), entry("kafka.key", TEST_KEY));
}