Extend lab 2 error handling

[altenstedt]

This is an issue that describes an idea for making the course better.

The chapter about error handling is a little short, and perhaps too shallow. We say that we will come back to the concept later. We might be better off keeping error handling more contained. Error handling is rarely done right, and it sparks discussions at the end of the course; We want to have more of that engagement at this chapter.

What we want is a chapter that more closely ends up where we are in the final lab 6. We want to show a design pattern that do not model error handling based on exceptions.

[erica-edholm]

I would like to join this session to get better error handling in the TDD 2 course