I was an engineer on the Visual Studio team. Internally, the Notepad project existed to provide a minimal, shippable product that we could use as a testbed. We used it to validate everything from compiler changes to kernel32 loader behavior on beta versions of Windows. If Notepad didn’t run, your feature didn’t work.

This doesn't seem like a good idea.

Well, you see, they got rid of all the QA so those tests stopped adding value ;)