How to add changes to the bot functionality in production?

Question

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The customer asked to add functionality to his bot, he has a lot of people using it, and often when I make changes in production, everything falls down and he stops responding to everyone if I made a mistake.
So: how to test a bot not in production? How to be in this situation? So that I first saw the changes, and only then, if everything is fine, should they be transferred to production? (VK callback API)

Answer 1

emulate callback requests with self-written scripts
proxy real callback requests to a separate host with the tested version

Answer 2

Green Blue Development