Static typing combined with functional programming is superior to automated testing, although the three are actually complementary, because automatic, property-based testing works better if you have type info (such that the library knows what values to generate) and referential transparency, because side effects can be awkward to specify as laws.

So it is not a coincidence that Haskell developers have innovated testing tools and are now sold on QuickCheck, those two working well together ;-)

Being the Scala developer that I am, I love ScalaCheck, but I’ve also used jsverify for JavaScript ... not as good as ScalaCheck or QuickCheck, due to not having static typing and type classes btw, but did the job.