Provided is a test method by which a transistor whose reliability is low can be detected with low stress and high accuracy in a shorter period of time than a BT test. Provided is to detect a transistor whose reliability is high in a shorter period of time than a BT test and manufacture an electronic device with high reliability efficiently. Hysteresis characteristics revealed in the result of the Vg-Id measurement with light irradiation to the transistor correlate with the result of a BT test; whether the reliability of the transistor is Good or Not-Good can be judged. Accordingly, the test method by which a transistor whose reliability is low can be detected with low stress and high accuracy in a shorter period of time than a BT test can be provided.