@Test void builder_merge_annotations_concat() {
    Span merged = Span.newBuilder().addAnnotation(1, "a").addAnnotation(1, "b")
      .merge(base.toBuilder().addAnnotation(1, "b").addAnnotation(1, "c").build()).build();

    assertThat(merged).isEqualToComparingFieldByField(
      base.toBuilder().addAnnotation(1, "a").addAnnotation(1, "b").addAnnotation(1, "c").build()
    );
  }
Catches common error when zero is passed instead of null for a timestamp
zipkin/src/test/java/zipkin2/SpanTest.java