Disclosed herein is a test circuit for a device under test. The test circuit includes a test data source and a test data target. A debug chain is coupled between the test data source and test data target, and operates in either a clock debug mode or a test mode. The debug chain, when in the test mode, is deactivated. The debug chain, when in the clock debug mode, receives the test pattern data from the test data source and stores the test pattern data, generates a clock debug signature from the stored test pattern data while clocked by a test clock, and outputs the clock debug signature to the test data target, the clock debug signature indicative of whether the test clock is operating properly.