Individuals can easily change interaction roles during everyday tasks, for example by shifting from following someone's lead, to leading the task themselves. We are interested in how these existing social experiences scale to human-robot interaction (HRI). How would robots change their interaction roles when working with people? Would changes in interaction roles pose a challenge unique to robots? In this paper, we propose a testbed for changing interaction roles in HRI based on a drama exercise known as the Mirror Game. The Mirror Game enables close collaboration between two individuals with each closely following the other's movements. Utilizing the Mirror Game with a large humanoid robot allowed us to examine people's reactions to changes in the humanoid interaction roles. We contribute: 1) the design of a human-robot interaction role-switching testbed based on the Mirror Game 2) a prototype of our testbed realized with Rethink Robotic's humanoid, Baxter, and 3) the results of a preliminary study examining people's reactions to the robot changing interaction roles to verify the design of the testbed.