Devon C. Estes:

It’s fairly common for folks who haven’t used mutation testing before to not immediately see the value in the practice. Mutation testing is, after all, still a fairly niche and under-used tool in the average software development team’s toolbox. So today I’m going to show a few specific types of very common problems that mutation testing is great at finding for us, and that are hard or impossible to find with other methods

He goes on to detail the “multiple execution paths on a single line” problem, the “untested side effect” problem, and the “missing pin” problem.

Phoenix 1.3 introduced the idea of Contexts, which I’m generally very much in favor of. However, I wish there was a little bit more structure to the idea. It’s so open ended that I’ve found deciding where best to put a function kind of tricky, and then I frequently end up with duplicate behavior across contexts or have a hard time finding functions later on because the module they’re in made sense at the time, but it doesn’t make as much sense now.

So, I’m proposing the idea of a Primary Context and a Secondary Context.

I’ve also struggled to determine just how to use Contexts to my benefit. It seems that Devon is trying an add more structure approach whereas I have (so far) gone with a YAGNI approach.