@Test void producerLinksToServer_sameSpan() {
    List<Span> trace = List.of(
      span("a", null, "a", Kind.PRODUCER, "producer", null, false),
      span("a", null, "a", Kind.SERVER, "server", null, false)
        .toBuilder().shared(true).build()
    );

    assertThat(new DependencyLinker().putTrace(trace).link()).containsOnly(
      DependencyLink.newBuilder().parent("producer").child("server").callCount(1L).build()
    );
  }
Servers most often join a span vs create a child. Make sure this works when a producer is used
instead of a client.
zipkin/src/test/java/zipkin2/internal/DependencyLinkerTest.java