My team (40+ QA Engineers) executes functional, integration and automation testing services for a large customer. We are not developing products, only test them. We test various applications built by variuos development teams (which are teams on customer side or other outsourcing vendors) and testers need to ajust their work with the methodologies and processes implemented in each of that teams (so it varies from true scrum approach to some kind of waterfall..). We have projects with Test Cases such complex that passing one integration TC through all front-to-back systems may take 1 day. We have projects with large number of UI-related regression test cases where tester can pass 100+ in one day
Having all this differences is it a documented way to define "Software Testing as a Service" operation model and to develop metrics that can measure team success and improvement in a long term run?