the system meets the needs of its customers and users (is it functional, reliable, available, responsive, etc.), and internal quality is how well it meets the needs of its developers and administrators (is it easy to understand, easy to change, etc.).” “Freeman, Steve. Growing Object-Oriented Software, Guided by Tests” / Chapter 1. What Is the Point of Test-Driven Development? https://www.amazon.com/Growing-Object-Oriented-Software-Guided-Tests/dp/0321503627 外部品質/内部品質