Diagnosing celiac disease after going on a GF diet

ould you clarify for me the different ways to test for celiac disease? If you have been GF for a while, would a biopsy then not indicate celiac disease? If you could educate me on the diagnostic tests for celiac disease AFTER you have been GF for a period it would be greatly appreciated!

Ancestry type testing for celiac genes

Is it possible to still have celiac disease without the gene? I really would like an understanding of the reliability of these offline genetic tests as they relate to celiac disease and what to do if one of these tests says that you don’t have celiac disease after all.