static StorageComponent buildStorage(final SpanConsumer spanConsumer) {
    return new ForwardingStorageComponent() {
      @Override protected StorageComponent delegate() {
        throw new AssertionError();
      }

      @Override public SpanConsumer spanConsumer() {
        return spanConsumer;
      }
    };
  }
Wait until all kafka consumers created by the collector have at least one partition assigned.
zipkin-collector/kafka/src/test/java/zipkin2/collector/kafka/ITKafkaCollector.java