Add tests to format-coverage command

[ale7714]

We want to add test to the format-coverage so we can test we don't introduce breaking changes.

[ale7714]

@markbates do you have tips on how to better test this? :)

[markbates]

The best way would be to do what we did with the upload command. Split it off into its own package that makes it more easily testable.

[mknycha]

Just wanted to check - Is it ok to contribute, or someone is already working on this issue?

[mknycha]

@ale7714 ⬆️