Wow. As a quality/test-related professional, aerospace and medical are the two contexts always cited as wanting heavy test design with waterfall process including coverage and validity review, formal certification process, etc. They’re canonical examples where you have to favor safety over business concerns—particularly deadline/release related. 

Boeing seriously fucked up here. This was a grossly unprofessional and obvious omission in a test plan. When you have “given a sensor reading is accurate, when X happens then MCAS should do Y” as a requirement, someone had better damned well test or at least quantify risk around what happens when it’s not accurate.

Maybe it’s my industry bias but this is way more damning to me than whatever the MCAS actually was doing. This one got found quickly because they managed to overlook an obviously fragile dependency that breaks a lot. What other more subtle corner cases are hanging out in Boeing planes waiting to auger you into the ground like a lawn dart?