This test generator takes data flow block diagrams and uses requirements-based templates, selective signal propagation, and range comparison and intersection to generate test cases containing test vectors for those diagrams. The templates are based on the functionality and characteristics of a block type, and each block type has associated templates. These templates provide maps for the creation of test values that verify the functionality of particular instances of that block type. Signal propagation allows the generation of diagram-level test cases that verify particular characteristics of a single embedded block. The methods disclosed for signal propagation utilize range intersection, equivalence classes, and block type formulae to create efficient and complete test cases. This test generation method would preferably be repeated until all blocks in a data flow block diagram were verified in their respective contexts, and it creates test cases that cover multiple time steps.