There are several tests that the courts use to determine whether a defendant is mentally ill. These tests are:

M’Naghten Rule/Test

The defendant must not know that his act was wrong; or not understand the nature and quality of the act.

Irresistible Impulse Test

The defendant is unable to control his actions or conform his conduct according the law.

Durham Test

The crime is a product of her mental illness. In other words, the crime would not have been committed if the defendant was not mentally ill.

A.L.I. or Model Penal Code Test

Defendant had a mental defect and lacked the capacity to appreciate the criminality of his actions or conform his conduct to the law.