Skip to main content

Should All Requirements Be Testable?

When product managers specify requirements for a product, we strive to formulate the requirements in such a manner that they are testable. Companies obviously want to know when they have developed a product that satisfies the requirements; to this end we want to provide testable requirements. Yet sometimes it is not practical to test a requirement directly.

Take, for example, the requirements for a new, super-reliable model of car. We might specify that the car should last seven years without repairs as long as the owner maintains the car according to a certain maintenance schedule and doesn't have a collision. But it is not possible to directly test whether the product meets these requirements without producing the car and driving it for seven years.

The difference is between requirements that are possible, in principle, to test, and those that are possible, in practice, to test. As product managers, we should strive for requirements that are possible to test in principle. We can't ignore market demands just because it's hard to test whether a product satisfies them.


For untestable requirements, you could similate approprimate tests. In your car example, this may mean stress testing components, similating weather conditions (e.g., putting the car in sub-zero conditions), starting it up 8,000 times and driving 60 miles each time etc... While not an exact match it might be close enough to give you some certainty.
Roger L. Cauvin said…
I agree completely, Marcus.

Just because it is not practical to test a requirement directly doesn't mean you can't test it indirectly through simulation.

A requirement always prescribes a test. Sometimes this test is not practical to carry out before releasing your product. In such cases, your team devises and carries out other, related tests that determine indirectly whether the product satisfies the requirement.

Popular posts from this blog

Why Spreadsheets Suck for Prioritizing

The Goal As a company executive, you want confidence that your product team (which includes all the people, from all departments, responsible for product success) has a sound basis for deciding which items are on the product roadmap. You also want confidence the team is prioritizing the items in a smart way. What Should We Prioritize? The items the team prioritizes could be features, user stories, epics, market problems, themes, or experiments. Melissa Perri  makes an excellent case for a " problem roadmap ", and, in general, I recommend focusing on the latter types of items. However, the topic of what types of items you should prioritize - and in what situations - is interesting and important but beyond the scope of this blog entry. A Sad but Familiar Story If there is significant controversy about priorities, then almost inevitably, a product manager or other member of the team decides to put together The Spreadsheet. I've done it. Some of the mos

Henry Ford's "Faster Horse" Quote

You may have heard the ( apocryphal ) Henry Ford quote: If I'd asked customers what they wanted, they would have said "a faster horse". Over at the On Product Management blog , Saeed gives his take on this infamous quote. He "hates" it, and gives some compelling reasons. Saeed is spot on in his explanations. Personally, I think the quote is great, but it's a matter of interpretation. The valid point of the quote is not that it's a bad idea to facilitate a conversation with your market to better understand it. The valid points are: You must ask the right questions to get valuable answers. You must interpret the answers thoughtfully - often outside their direct meaning - to glean reliable information. Asking questions is not always the best way to "listen" to your market. (E.g., sometimes pure observational studies are more reliable.) Nonetheless, I find the quote is helpful to combat "armchair product management" in the

Use Case as a Black Box

Consider the following use case: Purchase Items Actor: Purchaser Precondition: Purchaser types at least thirty words per minute and has a web navigation efficiency rating of at least 40. Postcondition: For the average Purchaser acting at full efficiency, the number of seconds elapsed is no more than 30 + 20 * n, where n is the number of items purchased. The name of the use case represents a functional requirement. What does the product do, or enable the user to do? Purchase items. What are we to make of the preconditions and postconditions? What relationship do they have to the requirements for the product? Answer: the preconditions and postconditions are the nonfunctional requirements attached to the functional requirement . Another way of expressing the nonfunctional requirement would be as an attribute and associated constraint: Usability: For a Purchaser who types at least thirty words per minute and has a web navigation efficiency rating of at least 40, it shall take no