Your testing was not exhaustive - it failed cuz you didn't adequately load test it.

Next.
Let's hit one missile before you decide to scrap the whole thing. This is what this type of testing is for. To see if the damn thing works. You start slowly and work up.
Next.
Your underlying premise is a joke.
Say your shield was designed to eliminate all of Russia's ICBMs. How ya gonna test it? In your world you would ask Russia nicely to disarm all their missiles and fire them all off at once, asking them to miss populated centers by only a couple of miles so that you dont accidentally kill someone if you miss one. Do you yet see how flipping ridiculous this is?

In the real world, you make sure you can hit one. when you've perfected that, you try to hit two. Then 3 and so on, until you reach a number where probability dictates that you'll hit more if you have to.

Jeebus, I don't even particularly like the missile shield system, let alone agreeing with both Tom and Larry at the same time. ;-)