> There's a black art into estimating what angles to test and how deep to avoid calcification. There may be a black art to recognizing what you overlooked, but

> There's a black art into estimating what angles to test and how deep to avoid calcification. There may be a black art to recognizing what you overlooked, but otherwise it is pretty straightforward. Tests are your documentation. The angles needed to be covered are exactly what the user needs to know to use your software – how to use it and, when using it, what happens both in the expected case and when failure occurs (especially what happens when failure occurs!). Calcification is of little concern as the inverse is breaking changes, and the user does not want to deal with your breaking changes. You can put your mind at ease knowing that once you commit to a documented feature, it should remain there until the end of time.