While intelligent agents offer substantial potential when integrated into human teams, challenges persist in achieving effective collaboration and information sharing with these systems. A virtual testbed of modular design was developed to enable rapid implementation of different teaming behaviors, comprehensive observation and measurement of individual and team performance, and flexibility of team composition, task objectives, and environment configurations. Using the testbed, an initial study demonstrated that in a non-hierarchical collaborative task, sharing information among teammates improved task performance and the ease with which to work with autonomous teammates, while reducing participants' mental workload, as measured by the NASA-TLX survey.