Abstract: Apparatus and method for testing electrical circuits, especially printed circuit boards containing a number of integrated circuit components. Access to the component to be tested is by means of a clip with driver/sensor pins having field effect transistor circuitry. Each pin corresponds to an access point on the device under test, and each pin includes its own circuitry for driving the inputs and sensing the outputs of both analog and digital components. The test instrumentation is integrated with a host microcomputer, eliminating the need for "memory behind the pins". Test programming directs the test instrumentation to perform functional testing while the components are in circuit and to test for in-circuit component parameters. The invention provides automatic test generation, including means for learning the characteristics of known good components and boards.