That's the worst thing to do: doesn't provide any value at the part that matters.
It may worth to improve code quality where it matters (the business logic), but to improve it where it doesn't matter is a waste of time to both the employee and the employer
Only noobs like myself years ago would go ahead and refactor a lot of code during work hours without a good reason.
However when you stumble through something and finally understand the idea behind it (good or bad) then it might be a good time to add a couple of tests.
And when you have a few tests that covers nearby code you can hopefully find the courage to make a few surgical cuts to remove the worst tumors. ;-)