Chapter 2.1 misses a remark that getters for instance variables are needed

[jpeinelt]

When you follow the chapter 2.1 to construct the CustomerSatisfactory UI and you hit 'Play' in the Playground after

| ui |
ui := CustomerSatisfactory new openWithSpec.

you will get a does not understand: #buttonBad debugger window. This is because the book does not mention that your objects need getters for the UI elements referenced in the defaultSpec method.