Earlier quoted context omitted.
No tests? Just mess up some mundane detail [1] and voila! Wake-up calls and heart attacks for 100,000s of administrators? 1: "Oh, well, this is not a mundane detail, Michael!" https://www.youtube.com/watch?v=3fGHaVn5rGo
There will have been tests, but there will have been missing end-to-end tests. Test 1 will verify that the new system/product emits billing entries in some expected way ("We did 100 bytes of operations and we see we called the billing system for 100 bytes of stuff, yay, test pass"). Test 2 will be in the billing system ("We provide an incoming bill for SKU#12345 for 100 gigabyte-units and we see it costs $17, yay, te…
Unfortunately "automatic generation" of unit tests have made a big part of the value of unit tests ("I am telling you what I expect here") disappear.