Disclosed herein is a method of testing a substrate. In the method, a first test terminal is connected to a first external circuit layer coupled to a first connection pad of a first active element included in a substrate, and a second test terminal is connected to a second external circuit layer coupled to a second connection pad of the first active element. Static electricity is applied through the first test terminal and a voltage drop of an electrostatic discharge protection circuit of the first active element is measured at the second test terminal, thus testing a status of a connection between the first active element and the external circuit layers. In the method, status of a connection of a connection circuit layer, a connection of an external circuit layer, a connection of a surface mount element, and a normal operation of the substrate is further tested.