You write unit tests and ensure 100% code coverage. Let's image this counter scenario: You write a couple unit tests for your most common cases and a couple co

You write unit tests and ensure 100% code coverage. Let's image this counter scenario: You write a couple unit tests for your most common cases and a couple corner cases. You don't even try for code coverage over ~80%. For me, the second case is more common. I simply don't have the time to keep the unit tests up to date with every iteration. In these cases I like static typing as it finds errors I miss.