Is there a test for starch allergy's? are there treatments for starch allergy's (other then simply avoiding them)?

Yes: It is usually the protein in the starch causing the allergic reaction. There is currently no FDA approved treatment for food allergy although sublingual and oral desensitization has been tried with variable success. The current approach remains avoidance.

Not really: There is no test for starch allergy per se. There are skin tests and blood tests for certain foods that may contain starch like potato and grains. These tests are for IgE mediated allergies which cause symptoms like hives, swelling, difficulty breathing, GI symptoms, etc. No treatment other than avoidance at this time.