The level of experience of the people writing (and maintaining) the code is also a factor I think. As other commenters have said it's all about risk reduction.

The level of experience of the people writing (and maintaining) the code is also a factor I think. As other commenters have said it's all about risk reduction. I definitely agree that you can get a lot of value writing integration tests. At the same time I'm a slightly concerned that if I'd read this article when I was first starting out as a developer I'd have thought unit tests were a side-note or a chore, rather than the building blocks for an application.