This Recommendation provides a common approach to the specification of OSI conformance test suites. It describes the process of developing an Abstract Test Suite (ATS), including the design criteria to be used and guidance on its structure and coverage. The text was developed jointly with ISO/IEC JTC1 and the main intent of this revision is to reflect the changes as a result of the work on Protocol Profile Testing Methodology (PPTM) and on Multi-Party Testing Methodology (MPyTM).