The increasing numbers of hybrid electric and full electric vehicle models currently in the market or in the pipeline of automotive OEMs require creative testing mechanisms to drive down development costs and optimize the efficiency of these vehicles. In this paper, such a testing mechanism that has been successfully implemented at the US Environmental Protection Agency National Vehicle and Fuel Emissions Laboratory (EPA NVFEL) is described. In this testing scheme, the units-under-test consist of a battery pack and its associated battery management system (BMS). The remaining subsystems, components, and environment of the vehicle are virtual and modeled in high fidelity. The complete testing system includes the battery pack, battery management system, battery cycler, battery test automation system, and hardware-in-the-loop (HIL) simulation platform that includes powertrain simulation software, vehicle dynamics simulation software, and various electronic systems for real-time model execution and communication. In the HIL simulation platform, first the roads and maneuvers which the vehicle will follow are defined with related traffic conditions. The intelligent driver in the vehicle dynamics simulation software sends control commands to the powertrain simulation software to achieve the reference maneuver on the given road. The desired battery power calculated in the powertrain simulation software is transmitted to the battery cycler for execution. As seen from the list of software packages and hardware/software components contained in this test system, ensuring that all of these components and subsystems (virtual or real) function seamlessly in real-time is a significant challenge. In addition to the system architecture and its benefits, these challenges and how they are solved are described in detail.