Focusing on development and then on testing

I find it liberating to focus separately on developing and testing. When I am coding a feature, I do not want to be distracted by obscure corner cases. If I think of one, I take notes so I do not forget to test it later. However, I prefer to focus all my energy on the business rules I am implementing and, at the same time, ensure that the code is easy for future developers to maintain.

Once I am finished with the coding decisions, I focus on testing. First I follow the different techniques as if I were working my way down a systematic checklist. As you saw in the example with Eleanor, she did not have to think much about what to exercise when the method received a list: she responded as if she had a checklist that said “null, empty list, one element, many elements.” Only then do I use my creativity and domain knowledge to exercise other cases I find relevant.