@Test void linksSingleHostSpans_errorOnClient() {
    List<Span> trace = List.of(
      span("a", null, "a", Kind.CLIENT, "web", null, true),
      span("a", "a", "b", Kind.SERVER, "app", null, false)
    );

    assertThat(new DependencyLinker().putTrace(trace).link()).containsOnly(
      DependencyLink.newBuilder().parent("web").child("app").callCount(1L).errorCount(1L).build()
    );
  }
Client+Server spans that don't share IDs are treated as server spans missing their peer
zipkin/src/test/java/zipkin2/internal/DependencyLinkerTest.java