@Test void constructsTraceTree_dedupes() {
    List<Span> trace = List.of(
      Span.newBuilder().traceId("a").id("a").build(),
      Span.newBuilder().traceId("a").id("a").build(),
      Span.newBuilder().traceId("a").id("a").build()
    );

    SpanNode root = new SpanNode.Builder(logger).build(trace);

    assertThat(root.span())
      .isEqualTo(trace.get(0));
    assertThat(root.children())
      .isEmpty();
  }
Same as {@link #constructsTraceTree()}, except with shared span ID
zipkin/src/test/java/zipkin2/internal/SpanNodeTest.java