Hence the famous joke at NASA that you get to launch the rocket when the documentation if piled up would be taller than the rocket itself.
...all of which is just an excuse to show this great picture of Margaret Hamilton [1] lead developer on the Apollo guidance system standing next to (and slightly shorter than) the printouts of the source code https://en.wikipedia.org/wiki/File:Margaret_Hamilton_-_resto...
I've worked on some interesting software with lives on the line as well and the amount of test code absolutely dwarfed the functional part. I wonder whether at the time of the effort you linked that was already common practice and if it was what the fraction of that code was tests.
Assuming she's 1.65 meters tall and 66 lines per page (quite common back then), at 0.2 mm thickness per page that's 8K pages times 66 lines / page is ~550K lines. Pretty impressive!
