You can't really test a rocket until you fly it. You can ground test subsystems and components all you want, but that's not a system-level test of a rocket. The only true system-level test of a rocket is to fly it. When you deal with volatile hypergolic substances subjected to extreme conditions all flowing through a complex system-of-systems that have never been through integrated testing together, you are going to have some spectacular failures. Doesn't matter how much money you have or how clever your engineers are or what a quality organization you've implemented.