That's primarily the reason why there are no "concrete examples", because one person's concrete example is another person's definition of contrived. Splitting hairs over some toy example wasn't something I thought would buttress the ideas presented, though I can imagine why some might need that scaffolding to follow along.
Re resting - here are some points the article makes about how smaller functions can in some cases hurt testing:
1) "Furthermore, when the dependencies aren’t explicit, testing becomes a lot more complicated into the bargain, what with the overhead of setting up and tearing down state before every individual test targeting the itsy-bitsy little functions can be run."
Disambiguating this for you, one of the myths of smaller functions is that they are easier to test. The article makes the claim that this isn't always true, because many who wax lyrical about the beauty of smaller functions also champion for fewer arguments to be passed to the function. The book Clean Code very explicitly states this (read the book, not as a how to guide but as a cautionary tale), and many a time what I've seen happen in the wild (especially in Ruby) is that programmers who like small functions and don't like making deps explicit - which then means the code (and ergo tests) rely on setting up shared global state.
Of course one can write smaller funcs with fewer args and not do this, but that's not the point here. The main argument is that making functions smaller doesn't always make it easier to test.
The article also does provide two examples when having the smallest possible function does help in testing. I'm not going to rehash those arguments again here.