Imke Feldmann has a lengthy Power Query script to help debug issues with DAX variables:
When you’re dealing with a beast like DAX you can use any help there is, right? So here I show you how you can debug DAX variables who contain tables or show the result of multiple variables at once. So you can easily compare them with each other to spot the reason for problems fast.
Please note, that currently only comma separated DAX code is supported.
Click through for a demo as well as a video.