When you are developing a module for the Drupal AI, nothing is as frustrating as having to wait for the OpenAI or Anthropic provider, when you know what the response should be. You are only interested in solving your code, but you have to waste money and time using a real provider.
And then you want to run Kernel and Function Testing against your newly developed module, but you do not want to put your API Key in the CI and you do not want every test to run an actual call against the provider. It will cost money and the provider could have availability problems.
Drupal AI solves this with its own mockup provider AI Test, that exposes a mirror provider you by default - you say Jump, it say Jump. But it can also be used to record actual responses from the AI and replay them over and over, when you are developing or when you are running tests.
The AI Test module is part of the AI Core module and can be used by anyone extending it.