The 50% heuristic comes from a story I read once about a company claiming they were able to build a ~200 kloc app in a dynamic-typed language. The secret was t

The 50% heuristic comes from a story I read once about a company claiming they were able to build a ~200 kloc app in a dynamic-typed language. The secret was their ~200 kloc unit test suite. :) It has nothing to do with argument types per se, just that one must have very high coverage in order to be able to be reasonably sure that their app won't crash after minor code changes. In my current project we can get away with having integration tests cover a lot of ground and only unit test what makes sense thanks to static typing. High coverage is good to have, but should be balanced with test development and maintenance effort.