Summary

• We define a "tester" as someone who not only tests but who has QA and development skills.

• Our use of the term "tester" involves both QA and QC activities, and we drop the distinction between the two and encompass both in the integrated testing activities of XP.

• A tale of remodeling in which the contractor did not appreciate how the presence of a doorway in the plans should imply a door illustrates how customers' assumptions get missed in the development process.

• A tester makes a contribution by viewing the system from the standpoint of the customer but with the grasp of details, possibilities, and constraints of the developer, avoiding the "missing door" syndrome.

• A tester provides a skeptical outlook on the correctness of the system that helps keep the team from overlooking things that will make the customer unhappy.