Weaver      It is impossible to give you any guess to particulars on the test without knowing the type of work the prospective company does but:  I will try to shed just a small amount of light on the possibilities of the testing.  

More then likely you will have to do multiple coupons per alloy group, 3-8.  These usually will have a minimum thickness set and maximum thickness set.   For manual GTAW welding you could be looking at  .020-.032   to  .125-.375    generally speaking.    They may or may not include the same set of joints in both sets.

EXAMPLE:  T6061   "Thin set"  6g on .500x.032 tube, 1f on .032 sh (without burn thru or suckback), 5g on .032 sh to .032x.500 tube, 1g on .032 sh (minimal distortion), "Thick Set"  1g on .250 sh, 1f  on .250 sh

That is just a general example of the types of joints you might encounter.  I know of one manufacturer who only requires a 1f and a 1g in each alloy group, but most places are going to qualify you out in much wider range.   

The types of material can be pretty wide but aluminum and SS are the most common.    You may encounter Hastelloy, Waspalloy, Inconel, Titanium and likely 4130 steel.

I hope that sheds a little bit of light on it.  Basically you should call them up and try to talk to QC or someone over the welding dept and get a better idea of what they are looking for   D17.1 is a standard, not a test, and it covers a lot of ground.   If you are good with the tig torch and not afraid of learning some new metals it could be a great thing for you to give it a shot.

good luck
Tommy