I've seen basically Mario in VBA in Excel, so I know it's real. "Show formulas" && [VBA, JS] vs an app with test coverage.

Are unit and/or functional automated tests possible with VBA; for software quality and data quality?

GSheets has Apps Script; which is JS, so standard JS patterns work. It looks like Excel online can run but cannot edit VBA macros; and Excel online has a JS API, too.