if your code is correctly designed the business case that change doesn't require most of the tests to change. I have modules that haven't had any changed in 7 years, and I don't expect there to ever be a business case to change them. Even the modules that change, most of them are changing to add a customization in a place/way where we normally add them, so no existing test needs to change to support the new business case. There are exceptions, but tests that change because the business case changed are a design smell in general.