There’s nothing to test when your data structure can’t represent an invalid state. So many tests are being basic stuff like checking nil & empty lists; basic ADTs can design you out of that whole host of invalid states. Further, if your language only allows side effects at the edges of the application & data types are immutable, you are way less likely to need all these mock utils or get unexpected changes to your data.
There’s nothing to test when your data structure can’t represent an invalid state. So many tests are being basic stuff like checking nil & empty lists; basic ADTs can design you out of that whole host of invalid states. Further, if your language only allows side effects at the edges of the application & data types are immutable, you are way less likely to need all these mock utils or get unexpected changes to your data.