What is testable code?

Almost two decades ago, in 2002, Microsoft acquired the Danish company Navision A/S, at that time a relatively recent merger of Navision Software A/S and Damgaard A/S. You could say that with this acquisition my testing journey started, because – after I rounded off my previous role as a technical trainer at the Dutch Navision Academy – I joined the former Dynamics NAV Global Development Localization (GDL) team at Microsoft as an application tester and documenter. Early 2005, I was taking part in two Microsoft internal, so-called, Engineering Excellence courses; one for new Software Engineers and one for Test Leads. It was a great experience, not in the least due to the enthusiasm and great experience of our trainer Tracy Monteith (https://www.linkedin.com/in/tracy-monteith-021868115/). There are many things I owe to him, but one of the most prominent things that has stuck with me ever since is the notion of testable code. I can still recall a certain...