The Next Generation Air Transportation System (NextGen) advocates the use of innovative algorithms and software to address the increasing load on air-traffic control. AutoResolver [12] is a large, complex NextGen component that provides separation assurance between multiple airplanes up to 20 minutes ahead of time. Our work targets the development of a light-weight, automated testing environment for AutoResolver. The input space of AutoResolver consists of airplane trajectories, each trajectory being a sequence of hundreds of points in the three-dimensional space. Generating meaningful test cases for AutoResolver that cover its behavioral space to a satisfactory degree is a major challenge. We discuss how we tamed this input space to make it amenable to test case generation techniques, as well as how we developed and validated an extensible testing environment around AutoResolver.