Some at-home celiac tests require that you eat foods containing gluten for a specific amount of time before taking the test.
For example, the LetsGetChecked at-home celiac antibody test requires eating gluten for at least 6 weeks before taking the test. However, the company doesn't specify how much gluten to eat per day on their website.
Organizations like the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition recommend that a person eat about 10 grams of gluten — which is equivalent to 2 slices of whole wheat bread — per day for around 8 weeks before taking an antibody test.