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Testing

This really is a concept that you need to keep in mind when you write your code "testability". And i find that when you get this you also get a Buch of other properties for "free". Orthogonality and reusability for example. And really it's a force multiplier and kicks productivity into high gear when you know that your lower level components work as expected and you don't have to go ok a wilf goose hunt when something would be constantly broken. To summarize I find that writing tests early on reduce product velocity but the compound effect of good quality and regression prevention give you higher velocity later on.