You unit test the pieces, then integrate and system+regression test the product. Its got nothing to do with how you define unit - just a way to: 1) speed up o

You unit test the pieces, then integrate and system+regression test the product. Its got nothing to do with how you define unit - just a way to: 1) speed up overall testing and bug fixing 2) get better test coverage of units 3) stop wasting other team members time by testing your unit before saying it's ready for system test