I was in an interview and the interviewer asked me what I think about quality assurance, namely the QA. I answered with my fast thinking brain, falling back to the patterns I’ve used to ensure the product I build satisfies the quality requirements. Pretty usual stuff like testing, monitoring, alerting, etc. Of course there are several branching from each of them such as manual and automated testing, monitoring for performance, scalability, and for domain metrics, bug bashing before the product hits production. I counted many things I do as a software engineer. The answer I gave satisfied the interviewer and we moved on. After the interview was over, though, my mind was racing over quality assurance.

For most of my time in this world, quality meant “Made in Germany”. Outside of my job, I didn’t have a simple answer to this question: “What is Quality?” If something was made in Germany, that something shipped with a stamp of quality. I could feel the quality of a product, but couldn’t explain it. The German youghurt maker my wife’s parents got from Germany 50 years ago was still working. That was quality. The shower head produced by a German brand would give me the same water output as it did 5 years ago, while other brands slowly (or more often quite fast) degraded. I once asked a taxi driver in the Netherlands why he was driving a Mercedes. He told me no other brand would match the comfort while giving him more than a million kilometers range in car’s lifetime. It was his job to drive the car all day long after all.

There is a pattern here: Consistency. When we purchase a product, we are buying a promise: The product promises to solve a job. The user experience may differ but the promise needs to hold. For example, my older VW Passat was much more comfortable than my newer VW Golf. But Golf is much cheaper than Passat. Their main promise, though, is transportation. It has quality if it can get me from point A to point B under different conditions. If it leaks water when it’s raining, then the quality is not there. I want to get to my target without getting wet. If the car is getting flat tire due to bad road conditions, then the quality is not there. A more obvious one is the brakes: If the they don’t work reliably, the quality is not there. Most of the products in the market focus on the obvious ones. Noone will purchase the car if the brakes are known to be faulty. But a car has thousands of parts that need to work well consistently. When it does, we say it’s a quality car.

So, quality is consistency… under different conditions. Does it work as promised on day 1000 as well as on day 1? Does it work as promised when it’s really hot vs when it’s really cold? Does it work as promised when it’s windy, or raining, or hailing? Does it work as promised when several people are using it? What about thousands? Different products have different quality requirements; but I expect these requirements are consistently met when they’re embedded in the product’s promise. That’s when I call it’s a quality product.