I was programming for a quarter-century before I actually sat down and built acceptance-tests while I was writing code.   And the experience really startled me.   It took a lot more time, and it took a lot less time.   The difference was startling.

I admit it:   I hate to test my work.   “If it compiles clean, I’m done.”   I still have to force myself to do more.

There is a tradeoff to be struck.   There are no absolutes.   You cannot test everything, nor do you necessarily have to.   What seems to matter the most are the low-level primitives ... the stuff upon which everything else in the program’s whole world depends.   It is easy to redo a piece of sheetrock, but if the house has foundation problems it may as well be torn down.

But, yes, it is a mark of a good, healthy program-development culture that folks do test as they build.   (For one thing, it suggests that they have given some thought to what they are actually doing|going to do.)   What CPAN routinely does is a good example.