The test plan is the set of ideas that guides your test process. We use the term test strategy to refer to the set of ideas that guides your test design, throughout the project. Test strategy is an important part of a good test plan. It is the connection between your testing and your mission. The textbooks have plenty to say about the logistics and work products of testing, but not so much about strategy so that will be our focus in this chapter.
Ultimately there is only one reason you test: Something important might go wrong. Your test process exists to identify investigate, and report the risks that the product may fail. That's why you need to ask three questions, repeatedly, about your test strategy:
Why bother? Testing is expensive. Don't include activities in your strategy unless they address a risk that matters enough to spend time testing.
Who cares? Reasons to test are not laws of nature; they're rooted in the feelings and values of people who matter. Don't include activities in your strategy unless they serve somebody's interest.
How much? Some strategies are much easier to say than do. "We will test all combinations of printer features" is one short sentence that launches a thousand tests (or a hundred thousand). How much of that are you really going to do?
Test strategy is ...