Abstract: A formal testing methodology is outlined in this paper, that proves applicable to validation of architectural units in object-oriented models, and its use is illustrated in the context of the design of a robot teleoperation architecture. Automated generation of test cases to validate the functionality of the robot trajectory generation unit showcases the key features of this methodology. A disciplined use of UML state diagrams, to model the unit''s dynamics consistently with its static properties as modeled by class diagrams, enables one to provide such models with Input/Output Labelled Transition Systems (IOLTS) semantics, whence a rich machinery of testing theories and tools based on those theories become readily available. Our case study tells that, besides black-box testing of nal implementation units, white-box analysis of architectural units may greatly benefit from the exibility of parameterized I/O-conformance relations. Test purposes turn out to be a useful methodological link between functional requirements, which they are drawn from, and conformance relations, which they help one to instantiate, thereby delimiting test selection to purposeful tests. Contingent aspects of our methodology include: a mechanical translation of state diagrams in Basic LOTOS, a non-mechanical, use-case driven synthesis of test purposes, expressed in the same language, and the use of the TGV tool for automated test case generation. Other choices in these respects are well possible, without a ecting the characteristic traits of the proposed methodology, that are rather to be found in: 1) the combination of object-oriented architectural modeling with IOLTS semantics; 2) the aim at maximizing the potential for test generation from UML models, in a broad view of testing which applies throughout the development process; 3) the speci c proposal to consider internal actions as testable actions, in view of a better coordination between testing (discovery of faults) and debugging (discovery of internal sources of faults). [Copyright &y& Elsevier]