While the advice seems well-reasoned and complete, I am not sure how the test-before-you-implement philosophy extends to GUI/graphical development. I work on h

While the advice seems well-reasoned and complete, I am not sure how the test-before-you-implement philosophy extends to GUI/graphical development. I work on high-level embedded applications where we design and simulate the application on the development machine before flashing it on the target. The usual test method would be to compare the expected/actual images and check to see if everything matches the requirement. In this case though, usually it is not possible to test something automatically before implementation since there is nothing to compare the results (images) with. Can anyone suggest how TDD-like methods work in this case?