This document summarizes a case study on usability testing of the Primo discovery tool at Imperial Library. It discusses two rounds of qualitative user testing to understand how users search for and discover resources. The first round found that library search meets expectations but discovery happens elsewhere. It also identified issues in navigating from search results to full text. The second round used interviews and card sorting to understand how to improve search speed and information presentation. This led to changes like a simplified search box and prioritizing facets. The new version of Primo was launched after testing, along with lessons about involving staff and accepting design decisions.