Test patterns for testing electrical circuits are generated by a MUX having its output operatively coupled to a Scan-In shift register and inputs receiving seed pattern signals, response signal from a response shift register, positive and negative signals from the Scan-In register. A control logic circuit provides control signals that enable the MUX to select appropriate input signals. The circuit arrangement enables relatively few seed patterns to generate relatively large number of test patterns. The seed patterns are a sub-set of a test pattern set preferably generated by software such as the Automatic Test Pattern Generator (ATPG). A method to generate the seed patterns is, also, provided.