This report describes the FAIR-IMPACT Milestone M5.1 - Reference collection of test data sets, one of the outputs of Work Package 5 - Metrics, certification, and guidelines. The Milestone consists of a collection of links to social science data sets. These are intended to verify the implementation of the discipline-specific metrics for the social sciences which are also being developed in the same Work Package. Note: The collection is currently available internally for the project partners only. After the initial testing with F-UJI and further curation of the collection, the collection will also become available to the larger public.