The correct term for testing a rear window grid is to test for Brilliance. In reality you are testing it like you would any other wire, but in the early days of window grids, like the late 60's, the term Brilliance was introduced and is still used by some.

Using this term in a Google search will return a number of sites.

But this video is a good place to start. You can use any voltmeter for this; a Fluke is not necessary but it is an easy instrument to work with.

How to use a Fluke 233 to test a rear window defroster - YouTube