AbstractA combination of three approaches is proposed here to validate the functional equivalence of re‐engineered programs. These are: control path comparison; data result comparison; and data flow comparison. Two of the three approaches are based on the theory of program slicing. The third approach is based on the theory of data invariance, i.e. the same input must produce the same output. Together, these techniques can provide a cost effective regression test environment for large scale re‐engineering proje