The problem with that is the economics for many applications don’t favor elaborate test suites. If you’re building a saas software product where you can detect a bug, fix it, and deploy in a matter of hours, and wherein developer velocity is among your most important metrics, an elaborate test suite is a liability (note that the suite spot is not “no tests” but somewhere in the middle) as it makes changes slower. Dynamic languages work reasonably well for these categories of applications, although some static typing can help improve that iteration time.