How to simulate a real checkout to test a new smudge filter?

I am looking for a way to force smudge filter to run by simulating a real life checkout. Let's say I just created a new branch and did not modify any files but want to test my new smudge filter. According to some answers such as https://stackoverflow.com/questions/22909620/git-smudge-clean-filter-between-branches and https://stackoverflow.com/questions/21652242/git-re-checkout-files-after-creating-smudge-filter it should be possible by running:

git checkout HEAD --

but in doesn't work with git 2.9.0. Method suggested in accepted answer here https://stackoverflow.com/questions/17223527/how-do-i-force-git-to-checkout-the-master-branch-and-remove-carriage-returns-aft works but I don't like because it seems fragile. Is there a safe way to do what I want to do in Git still today?