We have documented Service Test Management under IG1224 (https://www.tmforum.org/resources/standard/ig1224-naas-service-management-v8-0-0/).It covers both sequence diagrams & the functional context of TMF653. The Sequence diagram is at Level 1 so it only looks at the test specification and does not go beyond what is behind the specification (like Metric, etc).
GB1028 (https://www.tmforum.org/resources/standard/gb1028-end-to-end-performance-management-using-tm-forum-apis-v1-0-0/) shows how you can apply METRIC in the context of performance/quality and you can apply the similarly for Test. You can also refer to GB922 Metric document to get a deeper understanding of Metric ABE.There is no METRIC API at this point in time listed in the Open API Table (https://projects.tmforum.org/wiki/display/API/Open+API+Table). @Jonathan Goldberg Do you know if there is any Metric API proposal?