1. A computer program product for applying external clock patterns and external data patterns for LBIST in a simulator, with the computer program product having a medium with a computer program embodied thereon, wherein the computer program, when executed in a data processing system, causes the data processing system to: set up a simulation model in the simulator for a logic under test; set up an external LBIST block in the simulation model, wherein the external LBIST block comprises pre-verified internal clock and pre-verified data pattern logic; connect external clock inputs and external data inputs from the external LBIST block to the logic under test; determine the external clock patterns and the external data patterns to test the logic under test; apply the external clock patterns and the external data patterns to the logic under test; and receive and process output patterns from the logic under test, wherein the external LBIST block further comprises: at least one phase shift and spreader block (“PSSB”); at least one pseudo-random pattern generator (“PRPG”); and at least one LBLST controller clock pattern generator, wherein the LBIST controller clock pattern generator is coupled to the at least one PSSB and the at least one PRPG.