Abstract: A method and apparatus for using weighted random patterns in a partial scan test. A computer generates deterministic patterns on the partial scan design. Deterministic patterns that have the same number of capture clocks between adjacent scan loads are grouped together into pattern groups. A computer then determines a set of weights corresponding to each of the pattern groups. A tester then uses these weights as a filter to weighted random test patterns and applies these filtered weighted random test patterns along with the appropriate number of capture clock pulses to a device under test.