I moved my book to leanpub (as you may have guessed from the sidebar of this blog). The online version looks very good and is available for all, so I decided there is no point reproducing it on the blog.
Instead, you can read the new chapter called Why do we need composability? online on leanpub and maybe decide to download the current state of the book (which is an always will be free).
This chapter is a next step in explaining the object oriented design knowledge necessary to understand mock objects well.