Anywhere (@ref adding-tests-to-packages) appears, the link is broken.
It currently links to https://pkgdocs.julialang.org/dev/creating-packages/#Adding-tests-to-the-package
However, the "dev" version of the Pkg docs no longer has a section on "creating-packages".
Note "v1" of the Pkg docs does.
I would change this myself and submit a Pull but I can't figure out where to make the change.