@Override public MockResponse dispatch(RecordedRequest request) {
        MockResponse maybeFailure = failureQueue.poll();
        if (maybeFailure != null) return maybeFailure;
        MockResponse result = successDispatch.dispatch(request);
        if (request.getMethod().equals("POST")) {
          receivedSpanBytes.addAndGet((int) request.getBodySize());
        }
        return result;
      }
Starts up a local Zipkin server, listening for http requests on {@link #httpUrl}.

<p>This can be used to test instrumentation. For example, you can POST spans directly to this
server.

<p>See http://openzipkin.github.io/zipkin-api/#/
zipkin-junit5/src/main/java/zipkin2/junit5/ZipkinExtension.java