Magnet Polarity Tester for 10mm x 5mm Round Magnets

I have a project using 10mm x 5mm rare earth magnets to hold parts together. Since the magnets don't come marked, I wanted a simple way to determine the polarity so the parts attract, instead of repel.

I used these magnets:

https://www.amazon.com/gp/product/B01M0OKUIJ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1