[dahauns]

In practice, testing _all_ possible inputs is usually not a feasible goal, and often downright impossible (since it would mean solving the halting problem). While there are some languages and problem domains where formal verification methods are a possibility, for most of software development the best you can do is reducing solution space.

A sane type system would be a start for example. And it's no coincidence that functional programming and practices with emphasis on immutability are on the rise; Rusts ownership system is a direct consequence as well.

TDD _is_ important, if simply for enabling well-factored code and somewhat guarding against regression bugs. But - decades after Dijkstras statement (which someone has already posted in this thread) - the code coverage honeymoon finally seems to be over.