Very Short Blog Posts (30): Checking and Measuring Quality

This is an expansion of some recent tweets.

Do automated tests (in the RST namespace, checks) measure the quality of your product, as people sometimes suggest?

First, the check is automated; the test is not. You are performing a test, and you use a check—or many checks—inside the test. The machinery may press the buttons and return a bit, but that’s not the test. For it to be a test, you must prepare the check to cover some condition and alert you to a potential problem; and after the check, you must evaluate the outcome and learn something from it.

The check doesn’t measure. In the same way, a ruler doesn’t measure anything. The ruler doesn’t know about measuring. You measure, and the ruler provides a scale by which you measure. The Mars rovers do not explore. The Mars rovers don’t even know they’re on Mars. Humans explore, and the Mars rovers are ingeniously crafted tools that extend our capabilities to explore.

So the checks measure neither the quality of the product nor your understanding of it. You measure those things—and the checks are like tiny rulers. They’re tools by which you operate the product and compare specific facts about it to your understanding of it.

Peter Houghton, whom I greatly admire, prompted me to think about this issue. Thanks to him for the inspiration. Read his blog.