1. One or more computer-readable storage media storing instructions that when executed instruct a processor to perform acts comprising: collecting an execution trace resulting from software under test; extracting from the execution trace a sequence of actions; extracting from the execution trace observed data associated with the actions; generating code for a non-deterministic program (“NDP”) from the extracted execution trace; storing the observed data; performing a systematic program analysis of the NDP, starting from a path exercised by the observed data and extending into one or more different execution paths; and generating a test case comprising a set of inputs for each execution path.