I think what mentioned on the thread theoretically is good to test each individual part of the project, But even though all the parts work allow does not mean when you put them together it will guarantee to work. Product verification is to compare input vs output and make sure it fulfills a customer need. SO you need to check it at the end as a whole system. I believe what mentioned is more toward risk management and how to ensure and minimize any mistakes along the way for the project, With coordination with the PM. However, you need to have a final product or a sample unit to run the verification on it.