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

    assertThat(new DependencyLinker(logger).putTrace(singleHostSpans).link())
      .containsOnly(DependencyLink.newBuilder().parent("web").child("app").callCount(1L).build());

    assertThat(messages).contains(
      "detected missing link to client span"
    );
  }
Creates a link when there's a span missing, in this case 2L which is an RPC from web to app
zipkin/src/test/java/zipkin2/internal/DependencyLinkerTest.java