@Override public CheckResult check() {
    if (!server.isRunning()) {
      return CheckResult.failed(new IllegalStateException("server not running"));
    }
    return CheckResult.OK;
  }
Will throw an exception if the {@link Builder#port(int) port} is already in use.
zipkin-collector/scribe/src/main/java/zipkin2/collector/scribe/ScribeCollector.java