Unifying modal interface theories and compositional input/output conformance testing

Abstract

We present a novel formal foundation for model-based testing of component-based software systems, unifying principles from modal interface theories and input/output conformance testing. Our theory relies on Modal Interface Automata with Input Refusals (IR-MIA) as behavioral formalism for both the specification and the implementation under test. IR-MIA models allow for a fine-grained distinction between mandatory and optional, as well as between underspecified and forbidden input/output behaviors, thus improving expressiveness of existing approaches in various ways. The input/output conformance relation on IR-MIA, called modal-irioco, therefore supports positive and negative conformance testing with optimistic and pessimistic environmental assumptions and is preserved under modal refinement. Our theory further adapts a variety of different composition operators from interfaces theories to IR-MIA models, each enjoying—under moderate restrictions—desirable compositionality properties with respect to the modal-irioco relation. Those operators include interface conjunction for incrementally integrating multiple perspectives on the same component, as well as parallel composition with multi-cast and hiding for integrating multiple concurrently interacting components. Furthermore, a quotient operator on IR-MIA, serving as the inverse to parallel composition, facilitates decomposition of conformance testing, thus providing a solution to the unknown-component problem.