The patterns in this part are not "things" you'd see in an Ajax Appas in the previous partsbut processes you can use to aid development.[*] Diagnosis (Chapter 18) patterns help with troubleshooting and monitoring the health of an Ajax App. Testing (Chapter 19) patterns help with testing at various levels and are based on the agile practice of testing as the application evolves.
[*] If the idea of process patterns seems odd, feel free to treat them as general guidelines instead. There's actually a relatively long history of patterns for software process and practice; for example, see Jim Coplien's "A Development Process Generative Pattern Language" (http://users.rcn.com/jcoplien/Patterns/Process/).