This isn't the easiest to test. This code is historically in the renderer, and because it relates to dates and it's the dates that can be fruity, there no decent way to write a unit test, short of checking every single potential combination. I've written a quick test which runs through every day between 1/1/1970, and 31/12/2200 and confirms that the months are correct using the same code as supplied in the patch (but pulled out). Open the Calendar Click the "Calendar" link in breadcrumbs Confirm that the previous, current, and next months are shown Download https://gist.github.com/6dcb1811ecba88bdd89b5a1ba24ec7b0 and place in your dirroot Run is (CLI) Confirm that it only printed out a list of years, and did not print out any objects