The Ground Segment for Mission Operations is a complex System of Systems, including a significant variety of complex elements, often generic and reused across missions, following adaptation to meet mission or family of missions specific requirements and configuration. For such Systems of Systems, the availability of a reference environment where individual ground segment components can be deployed and tested throughout their lifecycle, both at subsystem level and in integrated test chains up to a complete End-to-End Ground Segment, is critical. Also the representativeness of such an environment is critical, in particular the representativeness of the test scenarios with respect to the end-user use cases. At the European Space Operations Centre, the End-to-End Ground Segment Reference Facility has been established as the one-stop environment where the System level Integration and Testing of the Mission Operations Infrastructure takes place. This paper provides an insight into the technical aspects of the End-to-End Ground Segment Reference Facility, the latest achievements, an overview of the remaining challenges and the outlook of its intended evolution.