I remember using something similar a long time ago - basically fuzz testing, I suppose you could call it property based testing where the property is "whatever

I remember using something similar a long time ago - basically fuzz testing, I suppose you could call it property based testing where the property is "whatever edits the user does, we should be able to save and reopen the document without crashing". It found so many bugs: file corruption, crashes, memory leaks, pathological performance issues. The kind of issues that standard unit testing doesn't find.