There is no test that can make a schizophrenia diagnosis. People with schizophrenia usually come to the attention of a mental health professional after others see them acting strangely.
Doctors make a diagnosis through interviews with the patient as well as with friends and family members.
Psychiatrists have the most experience with diagnosing schizophrenia. A psychiatrist or other licensed mental health professional should be involved in making a schizophrenia diagnosis whenever possible.
Substance Abuse and Mental Health Services Administration
This government agency was created to focus attention, programs, and funding on improving the lives of people with or at risk for mental and substance abuse disorders. This link will take you to their web site.