[AncientPC]

I can't find the links at the moment, but some HFT guys have responded to relevant Slashdot articles over the years.

From what I remember from those accounts, traders often like to tweak algorithms at the last second and there is little to no QA before changes gets pushed live.

It's sort of a byproduct of the necessity for speed. Algorithms are quite complex, and even running a basic test suite that takes a few minutes may be deemed unnecessary.