Network device operability testing is performed by defining a universe of possible device states as a combination of network coverages, available network services and possible subscriber features. In one embodiment, each individual combination of network coverage, for a particular service and feature collectively defines a particular device state for operability testing purposes. In one embodiment, test point data may be generated, where each test point corresponds to the device's operability for a particular device state. In another embodiment, state transitions and test point data may be represented as a node-based device state tree, which may navigated for pinpointing the nature and cause of device operability failures.