Ask HN: What developer tools would you like to see?

It's cool when you can build software and someone runs it on their own data just a short while later and has a direct line of communication to you, providing a tight feedback loop.

I quit my job a few months ago and in a few months I'll have to find a new one. I thought I'd see if anybody had any ideas for tools they wanted to see written that lined up with my interests and that I could try my hand at, to see if I could make a go of working on dev tools for myself before going back into the job market.

I love and hate unit testing. It's a fantastic idea that I've never seen successfully implemented in practice, mostly because the tests invariably fall by the wayside. At the very least, it's a burden to support them.

I'd love a tool that would observe my code during runtime - capturing all inputs and outputs from every function, as well as the value of each variable at each point in the execution flow. Because this would probably incur a performance hit, I'd want to have the option to toggle it on/off.

After execution, I can scroll through a list of called functions and decide which ones I want to save. Once I choose to save, the tool generates a unit test for the selected function. Since the tool is capturing I/O of all functions, it could retroactively mock each call within the function.

This would only be useful for deterministic functions, of course, and it would still be up to devs to document why the expected results are what they are. But my goodness it would be a time saver - one click unit tests. Yes please.