1. One or more tangible computer-readable media storing computer-executable instructions for causing a computer system to design filtering hardware configured to perform a method of testing an integrated circuit, the method comprising: receiving a plurality of compacted test response vectors from a compactor of a circuit- under-test, one or more of the compacted test response vectors having respective compacted test response values that are dependent on one or more respective unknown values; filtering at least one of the compacted test response vectors to remove the dependency of the respective compacted test response values on the one or more respective unknown values; and outputting at least one filtered test response vector.