That's a great point! It's also what makes refactoring so much easier. If I need to rename a method obj.f() to obj.g(), then I can do so safely knowing that no

That's a great point! It's also what makes refactoring so much easier. If I need to rename a method obj.f() to obj.g(), then I can do so safely knowing that no lingering references to f() remain in my code base (else they would fail to type as f() is no longer a valid method). As you say, 100% code coverage is unrealistic. Having maintained large applications in both static and dynamically typed languages, I feel that statically typed programs are far easier to manage for this reason - that if my code compiles then it means there exist no errors of a certain trivial class, such as typos and references to classes or methods that have been removed. There are still other errors to worry about, but mitigating those errors can be done effectively without needing to approach 100% code coverage.