I have an 8 year old beagle that has had about 5 accidents (peed) in her bed while sleeping. This started about 2 weeks ago. My vet can't find anything wrong with her blood or urine and has ruled out Diabetes Insipidus. After $400 of test and boarding with them so they could measure her water and urine, they want to now do a Dexamethasone (SP?) Suppression test to see if it is Cushings Disease. Should I wait it out a little longer and see what happens before spending more money on this test? After doing research on Cushings disease she doesn't show any symptoms other than the drinking and urinating.

Well, Although she may not appear to have any of the symptons except drinking & urinating, That still qualifies as symptons, Although this doesn't necessarily mean your pet might have cushings disease,

I think you should do a little more research, use more keywords to define your question.
Before spending money, You should always do research, A pets life is just as good as "Ours".

I hope this helps,