Summary

A fit criterion is not a test, nor is it the design for a test. Rather, a fit criterion is an unambiguous goal that the product has to meet. It is used as input to building a test case where the tester ensures that each of the product's requirements complies with its fit criterion.

The fit criterion is an unambiguous goal that the product has to meet.

Quantifying or measuring the requirement gives you a better opportunity to interact with your stakeholders. By agreeing on a measurement, you confirm that you have understood the requirement correctly, and that both you and your stakeholders have an identical understanding of it. You will also find quantifying it ensures that the requirement is both wanted and necessary.

Adding a fit criterion to a requirement encourages testers to participate in the requirements process. Testers should be involved early in the development cyclewe cannot stress this point enough. Testers can help you to specify the fit criteria. This is not to say that the testers should write the fit criteria. However, testers are the best source of knowledge about whether something can be tested, and whether the fit criterion contains the appropriate quantification. In other words, the testers act as consultants for the fit criteria.

The fit criterion is the requirement. The description you write is the stakeholder's way of stating the requirement. If your stakeholders are like most of us, they speak using everyday language. Everyday language is, unfortunately, often ambiguous and sometimes not precise enough. You need a supplement to the requirementa fit criterion that is stated in unambiguous, precise terms and, most importantly, uses numbers or a measurement to convey its meaning.

The fit criterion is the requirement.

Fit criteria are also a vehicle for reaching a consensus among multiple stakeholders. Your attempts to clarify and measure will almost always result in hidden meanings becoming visible, hidden requirements bubbling to the surface, and, most importantly, the stakeholders agreeing on what is needed.

You derive a fit criterion by examining the requirement's description and rationale, and determining what quantification best expresses the user's intention for the requirement.

Fit criteria are usually derived after the requirement description is written. You derive a fit criterion by examining the requirement's description and rationale, and determining what quantification best expresses the user's intention for the requirement. You may sometimes find that this close examination results in changes to the requirement, but these changes are for the better and should be considered quite normal. Their occurrence simply means the requirement was not properly understood in the first instance. With patience and persistence, and with the wise use of measurements, you can ensure that each of your requirements is unambiguous, testable, and real.