I haven't finished reading and had to make a detour into another article by the same author, so, probably, I will have to extend the comment, but so far this:

> Perhaps the limiting factor is just that knowledge of effective test techniques isn't very widespread

That linked to: https://danluu.com/testing/

But of course... the problem of testing is a lot harder than performance optimization... I'm surprised this comes as a surprise. Performance optimization has plenty of evaluation metrics by its very nature. Testing? -- I wish there was anything tangible at all... Because we have metrics for optimization, we have theories of optimization, i.e. we have a way of explaining how or what optimization should do. With testing? -- we are nowhere close to this point.

Another aspect of this disparity is that we also know how to sell performance optimizations. It's easy to write into an ad pamphlet that the version 2.0 of gobbledygook does 185% more gobbledygook than the 1.0! (The number faithfully copied from my cereal box!) With testing? -- How can you even tell the customer that the product was tested better? Swear on your life and cross your heart (twice, as opposed to the last time when you only did it once?)

In general, in the field, I've only have so far met with extreme pessimism about feasibility of "theory of testing" existing. Even though the need for testing goes without saying, the actual testing task is reserved for the least competent and there's little no no effort made to improve anything in this department as it's perceived to be a black hole in the budget: no matter how much you could spend on testing, the effect is likely to be the same.