There was indeed a lot of unit testing as well as very intense reviews of every single line of code. We used C and Linux as we needed an operating system that wouldn't kill people. You had to have a minimum of twenty years experience to work there. An upside was that there was no pressure at all about shipping the product before it was ready, even though we were well behind schedule. The downside was that you were allowed one mistake in your code. You were fired for the second one.