It is common practice for military hardware to be designed for testability; however, the testability of software is rarely considered. When software testability is addressed, the resultant design often does not readily support full coverage automated testing. Since software products must be tested to verify requirements are met, it only makes sense to consider software testability from day one of a project. Once the decision has been made to embrace the concept of designing testable software, there are best practices that enable a lean software development process. This paper will discuss 1) designing for software testability; 2) the automated software regression testing approach; 3) the correlation to Extreme Programming (XP); 4) Lean 123 costs and benefits; 5) an example of how to create an automated software regression test; and 6) the applicability of this approach to all software efforts.