Idea: Save output for tests that differ to allow retroactive saving

[TheZoq2]

When running a runt test which diffs from the previous version, it is a bit annoying having to re-run the whole test to save the result with the -s flag

https://crates.io/crates/insta solves this by creating .new files for tests that differ, and has a separate command insta accept to replace the old files with the new ones without re-running the test suite, perhaps that could be copied here?

[rachitnigam]

That's interesting! One possible concern is that it would pollute the working directories for the tests and the user would have to add *.new to the .gitignore to avoid the problem. Another option is adding these files to a .runt folder in the base repo which could allow us support things like a quick test mode where only previously failing tests would be run.