James Bach responds:
Testing is an exercise in discovering a lot of things, including interfaces. But it is more than just discovery, it is inquiry. Inquiry is action; discovery is an event. Inquiry is within my control; not so with discovery. But certainly, good testing involves a lot of discovery and a lot of interfacing.
James raises a good point, and helps clarify the “Discovering Interfaces” test technique. Discovery would follow inquiry, and action would follow discovery. Through inquiry, testers can discover testable interfaces, and look at the feasibility of testing through them. The tester can collaborate with developers and other stakeholders to decide if the project warrants testing at the level of a particular interface, or at another layer in the application. If it looks feasible, testers can begin developing test cases against that testable interface.
This is a technique that I would encourage testers to look at when they are working on test automation strategies. Merely looking at the GUI (the most obvious interface to test against), only shows a thin layer of the application. There are other testable interfaces that in many cases may be better test automation candidates.