Good stuff, I’m looking forward to the book. I once implemented a command-line oriented API tester for a videoconferencing standards API, and a bunch of developers starting running scripts against it to test all the stuff behind it. They had usable videoconferencing “applications” running just by calling DOS batch files.

You might want to reference my book “Debugging” somewhere in your patterns book. The 9 rules (and corollaries) in “Debugging” are at a more universal level than typical design patterns, but they are patterns just the same. Your API tester would come under the general rules “Check the plug” (check assumptions about everything including upstream and downstream API operation), Quit Thinking and Look, and Divide and Conquer.