> I don't necessarily disagree with providing context, but my concern is that comments eventually lie. If the business rule evolves (say the window moves to 5 days) the comment becomes a liability the moment someone updates the code but forgets the prose.

Yes, comments can drift out of sync with the code. That doesn't mean the comments were a bad idea; it just means the programmer didn't update the comments when they should have.

Similarly, even with zero comments, variable names can drift out of sync with their intended purpose, e.g. when they are repurposed to hold values that are different from what their name implies. Again, the solution is to rename the variable so it reflects its purpose (or possibly create another variable).

> This way, the 3 day rule is a hard requirement that fails the build if broken rather than a suggestion in a comment block.

What happens when a dev changes the test code, but fails to update the string "should_match_debit_with_credit_only_if_within_three_day_settlement_window"? That's effectively no different than comments being out of sync with the code.