What utilities can reproduce traffic?

Question

Software testing

Good afternoon.
We are developing a product, the functionality of which is largely focused on integration with external systems. Can you suggest utilities that can emulate an external system?. Those. first we "record" the real traffic. And then during the testing process, when requesting a certain server, the server returns the previously recorded traffic for us.

Answer 1

netcat
hping

Answer 2

Look towards Mock objects.
As you described, it should be a very simple system where you say 1 and it responds with 1. But I think yours is a little more complicated and uses sessions, various responses that need to be parameterized depending on the request, and so on.