Testing home built headers for leaks

[WSSix]

Now that I am in the process of making my own headers, it has me thinking of what I can or need to do to test the headers for leaks. I plan to coat the headers once finished. The last thing I want to do is cut up freshly coated headers. Anyone have some suggestions on ways I can test for leaks? I'd like to actually drive the car around a bit before coating them so I can verify that my clearances with the body etc, which are tight, are good enough. Will this affect the coating process later? I'm hoping I can just have the headers cleaned and sand blasted to get them back to a point where they can be coated correctly.

Thanks