Behavior is an unfortunate term, because the "London Style" TDD sometimes is described as testing behaviors: https://softwareengineering.stackexchange.com/ques

Behavior is an unfortunate term, because the "London Style" TDD sometimes is described as testing behaviors: https://softwareengineering.stackexchange.com/questions/123627/what-are-the-london-and-chicago-schools-of-tdd https://softwareengineering.stackexchange.com/questions/1236... Which seems like the exact opposite of what the talk is saying you should do.