CWRU has participated in a joint project with IBM in developing an internal regression testing tool called Test Manager. The objective of Test Manager is to aid in regression testing at the unit testing, integration testing, or function testing levels and also to produce a reduced regression test set to verify the software changes indicated by the user. A conceptual basis for the tool, called a firewall, and a description of the factors which influenced the design of the tool are given. The tool utilizes a Prolog database; a set of experiments that determined how that database should best be structured is described. Timing and space requirements and future work and enhancements to the tool are discussed.>