Robert C. "Uncle Bob" Martin gave a talk at RailsConf 2010 on that we can buy 1025 more computing power per device in 2010 in comparison to 1970. Now, the figure is debatable, but that it's at least an order twenty I agree with.
He went into testing for a short while, and, I gave it some thought. Should testing be a language feature? I am not sure of it. Do you need a testing set-up/bed for a program, or should you be able to define tests from within the language. Given the amount of tests I am writing now, the latter doesn't seem too bad to me. So, a test construct in the language is certainly an option, even if I think you can't really do without building explicit test beds outside of programs.