A theory of regression testing for behaviourally compatible object types

This paper presents a behavioural theory of object compatibility, based on the refinement of object states. The theory predicts that only certain models of state refinement yield compatible types, dictating the legitimate design styles to be adopted in object statecharts. The theory also predicts that standard practices in regression testing are inadequate. Functionally complete test-sets that are applied as regression tests to subtype objects are usually expected to cover the state-space of the original type, even if they do not cover transitions and states introduced in the subtype. However, such regression testing is proven to cover strictly less than this in the new context and so provides much weaker guarantees than was previously expected. Instead, a retesting model based on automatic test regeneration is required to guarantee equivalent levels of correctness.