Philosophical test strategies start with a philosophy or belief about testing.
Exhaustive Strategy
With an exhaustive test strategy, one assumes that everything and anything can and will have bugs. It is decided that the possibility of missing bugs is unacceptable and that management will support a considerable effort to find all the bugs. Attempt would then be undertaken to test extensively across the functionality, the quality risks, the requirements and whatever else one can find to cover. The essence of this strategy is captured in an old tester's joke, derived from the catchphrase on the back of the US currency: "In God we trust... all others we test."
Shotgun Strategy
With a shotgun strategy, one also assumes that everything and anything can and will be buggy. However, one accepts that it is infeasible to test everything. Since there is a lack of idea on where to find bugs, we test wherever and whatever comes to mind. Test attempts are randomly distribute within the given resource and schedule boundaries, like pellets from a shotgun.
Externally Guided Strategy
With an externally guided test strategy, one accepts that it is infeasible to test everything, nor to know where the bugs are. However, we trust that other people might have a good idea of where the bugs are. Therefore, we ask for their guidance and test according to their direction, including asking them to help in determining if the observed results are correct. Common guidance include developer, user, technical or customer support, help desk staff, business analyst, sales people and marketing staff.
If the underlying philosophies and beliefs behind these strategies are correct, they can be appropriate. For example, testing weapons systems like nuclear missile guidance software clearly requires an exhaustive strategy. However, when applied in inappropriate situations, they could lead to dangerously misaligned test efforts.
Sourced from Surveying Test Strategies: A Guide to Smart Selection and Blending by Rex Black, Testing Experience Issue 2-2008. Slight modification has been made to the original text.
