Hi Ralf,
we renamed the chapter "Refactoring, Testing, and Debugging". The new ToC will be updated soon and the content should be up shortly. In a nutshell, this chapter has more emphasis on refactoring: we discuss
patterns to apply in your code and how typical object-oriented design patterns can be refactored using lambdas
Regarding debugging, you can set break points in a lambda expressions as you would normally do in your code. However, make sure the lambda is on multiple lines so you can set a line individually. Similarly for a stream pipeline. Instead of writing:
stream.filter().map().reduce()
You should write:
stream.filter()
.map()
.reduce()
So you can set break points on the individual operations.
The Debugging section specifically discusses on to examine stack traces (lambda expression makes things slightly less readable) and how to debugg/log information in a stream pipeline using the operation peek().