Previous research in the area of behavioral synthesis of digital circuits has mostly concentrated on optimizing area and performance. We present a behavioral data path synthesis system, called Genesis, which is geared towards hierarchical testability. A test environment for each module in the data path is guaranteed during allocation such that it becomes possible to justify any desired test set at module inputs from system inputs, and propagate fault effects from module outputs to system outputs. Genesis provided 100% system-level testability for all the synthesized benchmarks with a three-to-four orders of magnitude improvement in test generation time as compared to an efficient gate-level sequential test generator. The area overhead of circuits synthesized by Genesis is usually zero over circuits synthesized by other behavioral synthesis systems which disregard testability. Genesis can also easily handle loop constructs in the behavioral specification.