Testing during the design phase can prevent defects later on. I recommend we verify three things...
1.Verify the design is good,efficient,compact,Testable and Maintainable.
2.Verify the design meets the requirements and is complete (specifies all relationships between modules, how to pass data, what happens in exceptional circumstances, starting state of each module and how to guarantee the state of each module).
3.Verify the design incorporates enough memory, I/O devices and quick enough runtime for the final product