The assertion is that they're lightweight formal methods. Or is the article (and the proceedings of SOSP '21 it links to) wrong?
EDIT: ah I see where there might be confusion--obviously a library for generating random test data and making assertions about code under test itself doesn't constitute anything like "formal methods" but the idea of using that library in the way described in the paper linked from the article does. But that's kinda always the thing about software libraries..
EDIT: ah I see where there might be confusion--obviously a library for generating random test data and making assertions about code under test itself doesn't constitute anything like "formal methods" but the idea of using that library in the way described in the paper linked from the article does. But that's kinda always the thing about software libraries..