A test generator and methods for generating tests from a hybrid diagram are provided. A hybrid diagram is a diagram that primarily uses one higher-level semantic notation with portions utilizing one or more secondary higher-level semantic notations. Example higher-level semantic notations are statechart notation and data-flow notation. A test generator processes the hybrid diagram without reducing the higher-level semantic constructs to lower-level semantic constructs. The test generator generates test-generation templates as needed based on the higher-level semantic model used in the diagram. The test generator uses the test-generation templates to generate tests for a system-performing device specified by the diagram. The generated tests may be executed automatically by a test driver or manually by a human tester.