Automation. If we look at the “economics” of testing, the value of testing is in the number of test cycles that can be run and the speed of how quickly they can be run after a modification. If we can run the tests very often and really fast, essentially after every modification, the cost of creating the tests (and test automation) becomes largely irrelevant.

The reverse is true in “traditional testing”. Because that testing, unfortunately, relies on significant amounts of human labor, it is very expensive to run. Any test comprehensive test run will take countless of hours of human work, and will take significant amounts of calendar time. As a consequence, it makes economic sense to collect a larger set of modifications to test at the same time. Because of time constraints, the actual tests executed will be optimised to most likely areas of failure, resulting in increased risk of regression errors going undetected in areas of lower scrutiny. It also, obviously, means that for many features the testing comes much after the actual development, and therefore decreases the value gained. And, I won’t even go into how bad humans are in repetitive testing. I was a test manager at one point doing exactly this, because I didn’t know anything better.

So, because of high costs of test execution, the focus is on the cost of testing, and that consideration trumps most other concerns. But the focus should instead be in the value seek to deliver through testing, and optimising that (as is the Agile credo in general).