Knowledge co-production is increasingly referred to as a means to reorganise expert work and generate policy support. Co-production processes bring together diverse expertise to explore environmental problems beyond epistemic or administrative silos. This re-orchestration of knowledge production is seen as critical for the attainment of sustainability transformations. However, little attention has, so far, been given to the ways in which co-production experiments entangle with the settings to which they are introduced. Drawing from the new sociology of testing, we suggest that knowledge co-production experiments can be fruitfully analysed as tests of established policymaking practices. This approach highlights the role of co-production processes as collaborative forms that intervene by re-orchestrating the analysis of policy-relevant relationships. Interviews of actors engaged with two transition arenas shows that the experiments qualified as new forms of expert involvement, sources of ontological disturbance, and as interruptions in policymaking that oscillates around project-based regional development and an environmental conflict. The methodology provides a relational sensitivity to analyse the interplay between co-production experiments and their settings.