@Test void storeSpansCallback_toStringIncludesSpanIds_noMoreThan3() {
    assertThat(unprefixIdString(collector.new StoreSpans(TRACE).toString()))
      .hasToString("StoreSpans([1, 1, 2, ...])");
  }
Tags in zipkin v2 model are stringly typed.
zipkin-collector/core/src/test/java/zipkin2/collector/CollectorTest.java