I think it's pretty much empty sophistry to suggest that open-source projects (those of real importance) get to where they are today “by luck and by chance.” The important stuff, that we actually seriously rely upon, gets subjected to intense peer-review as it moves its way along the source-code control systems on the way to a “blessed” release.

Even for CPAN there is “CPANTS,” the amusingly named CPAN Testing Service which systematically self-tests everything on everything. If you don't submit a module with a good set of automated test-suites, it's not going to attract much attention, if it even makes it into the library at all.

Serious open-source-ware is a professional product, which is going to be employed in professional work and which therefore must be up to that standard of excellence.

Seasoned developers quickly learn that skimping on testing is like skimping on automotive maintenance:   “you can pay me now, or you can pay me later.” Testing has to be something that you do while you are developing the project. Planning the whole thing has to be something that you do before(!) you start to build anything at all. Good documentation has to be part of it. Go the whole distance or don't go at all. Nobody wants – nobody can afford – “half-ass-ware.”

We don't teach that sort of thing in school. We should, but for the most part we don't. There is actually not too much instructional-time available for the degree-track curriculum within a standard two- or four-year degree program, so most of the time gets spent just pointing out the features of the machinery and teaching the student just enough that he can use the machine without slicing his fingers off. Finishing a homework assignment is an accomplishment. But when you move into the profession itself, everything changes.