@Test void csWithoutSaIsServer() {
    DependencyLinkV2SpanIterator iterator =
        iterator(newRecord().values(traceIdHigh, traceId, parentId, spanId, "cs", -1, "s1"));
    Span span = iterator.next();

    assertThat(span.kind()).isEqualTo(Span.Kind.SERVER);
    assertThat(span.localServiceName()).isEqualTo("s1");
    assertThat(span.remoteEndpoint()).isNull();
  }
Dependency linker works backwards: it is easier to treat a "cs" as a server span lacking its
caller, than a client span lacking its receiver.
zipkin-storage/mysql-v1/src/test/java/zipkin2/storage/mysql/v1/DependencyLinkV2SpanIteratorTest.java