This is nothing new. I followed kernel development pretty closely about a decade ago and I was honestly very disappointed in what I saw. It's all about features, features, features, and there's almost no testing beyond "well, it works on my machine". It's kind of ironic that Linux has become the C++ of kernels, given Linus's feelings about C++: a giant pile of features, many of which nobody really understands, that can have some really weird corner case interactions.
I switched to FreeBSD as a result of my time reading LKML. The BSDs seem, at least to me, to be more designed rather than thrown together; but maybe I just haven't spent enough time watching their sausage get made.
Hopefully now that a senior kernel developer (Chinner) is saying some of these things publicly, things can get better. But a culture change of the magnitude needed will not come quickly.
However saying that no testing happens in Linux kernel is dishonest, to say at least: there is automated tests maintained by big corporations like LTP [1] or autotest [2], thousands of people run different versions of unstable/mainline kernels with different configurations, security researches does multiple tests like running fuzzers and reporting issues, multiple opensource projects run tests in current versions of Linux kernel (that in the end also serves as a test of kernel itself), etc etc.
Linux is basically the kind of project that is big enough and impactful enough that naturally gets testing for free from the community.