No, I'd maybe run them once just to check it covers the corner-cases. The code is never going to change, because it's a polyfill for old browsers, and only need

No, I'd maybe run them once just to check it covers the corner-cases. The code is never going to change, because it's a polyfill for old browsers, and only needed for legacy environments that won't change. So if the tests pass once, they'll pass forever. There is literally no point in adding those tests to my test suite - there is no combination of changes that will ever make this fail if it passes once.