It has been proven hundreds of times over that there is no test for a chemical imbalance in the brain.  Every once in a while some article will suggest that scientists are on the cusp of discovering one to give some credibility but to date there is no such test.

Psychologist Bruce Levine, Ph.D., concurs: “Remember that no biochemical, neurological, or genetic markers have been found for attention deficit disorder, oppositional defiant disorder, depression, schizophrenia, anxiety, compulsive alcohol and drug abuse, overeating, gambling, or any other so‐called mental illness, disease, or disorder.”