Tiny integration test change

It's a tiny change.

I've been following this project for a while as a hobby, also want to contribute to it. 

Currently I am going through test cases to learn. Found some tiny problems as we are testing "concat", we should care not only the total number of elements, but also the sequences.

Creating this request mainly want to make sure I am writing/commiting code to the correct place.

Let me know if there is any problem.

Best Regards,
Mingtao