We propose a non-scan design-for-testability (DFT) method at register-transfer level (RTL) based on hierarchical test generation: the DFT method makes paths in a data path single-port-change (SPC) two-pattern testable. For combinational logic in an RTL circuit, an SPC two-pattern test launches transitions at the starting points of paths corresponding to only one input port (an input, which has some bits, of an RTL module) and sets the other ports stable. Hence, during test application, the original hold function of a register can be used for stable inputs if the hold function exists. Our DFT method can reduce area overhead compared to methods that support arbitrary two-pattern tests without losing the quality of robust test and non-robust test. Experimental results show that our method can reduce area overhead without losing the quality of test. Furthermore, we propose a method of reducing over-test by removing a subset of sequentially untestable paths from the target of test.