Welcome Rosey.
Actually, it's very encouraging that your new GP practice wants to investigate you properly - a repeat test, after a few weeks on metformin (and perhaps a reduction in body weight, through chenge of diet and increased physical activity, although you don't mention this?) may result in a modified diagnosis. You may be able to continue on diet or exercise only, or you may have type 1 diebetes (which tends to develop more slowly in adults than children), LADA or MODY.
As mcdonagh47 says, it depends on what type of test is being proposed eg fasting blood glucose levels, OGTT (oral glucose tolerance test - 2 blood tests, 1 fasting, then another 2 hours after drinking a fixed amount of glucose) HbA1c (gives average measure of blood glucose over past few weeks), GAD antibodies / C-peptides (to decide between type 1 / LADA / type 2 etc). IGT = Impaired Glucose Tolerance; IFG = Impaired Fasting Glucose, by the way.