Julia developers have utilities to test type stability in their packages, as commented in another post long ago. And new tools that improve it have been released since then, e.g. Cthulhu.jl, or JETTests.jl more recently.
However, I wonder to what extent those tools are used in package testing. Creating and maintaining such tests is an extra burden, so perhaps the majority of developers live happy without them, and they are mostly used in packages where performance is critical.
On the other hand, since type stability is a problem that propagates, developers who are concerned about it would like to know that the functions of the packages they depend are type-stable too. So I imagine that popular packages that are widely also take care about it.
But is this only guessing. Does anyone have more informed knowledge about this question?
And could type stability be a separate test target? I fancy about a work flow that would grant badges to signal that the package is tested for type stability. (Although I have no idea about how that might be done.)