How does the AI know what tests it should write? I think this is an interesting experiment but somewhat dubious. The way I see AI would best help software deve

How does the AI know what tests it should write? I think this is an interesting experiment but somewhat dubious. The way I see AI would best help software development is that I the programmer have a question about my or somebody else's code, which the AI then answers, sometimes with a code-proposal but not always. It should be able to answer questions like "Is there a way to simplify this code? What are some inputs that would cause an error?" etc. AI should help us understand the code, and understand how to improve it. Not write all of it on its own because if we don't tell it what to do, it cannot know what we want it to do. Tests is a good example. What do we want it to test?