We present result from laboratory testing of a compact Energetic Particle Detector capable of making particle measurements in a variety of heliospheric and planetary environments. This ion composition telescope utilizes a novel electron-optics design and newly developed microcircuits to achieve combined directional particle flux measurements and high resolution mass spectroscopy in an extremely lightweight and low power package. The detector design provides for a high geometric factor and reasonable directional capability while maintaining excellent resistance to background radiation due to its small size and specialized coincidence logic. The prototype device, with an integrated time-of-flight custom integrated circuit, has been extensively characterized with electronic pulsers, radioactive sources in a vacuum chamber, and accelerator particle beams, revealing performance which substantially meets all requirements for mass resolution, bandwidth, power consumption, and weight allocation. A flight version would provide comprehensive measurements of the energetic particle environment on a mission where payload mass is tightly constrained, such as solar probe or a discovery-class mission.