Actually, no that isn't permitted, not in the contract with whichever responsible prime contractor is doing the job (can't speak for SEMs cos I dunno)
A MAW, for example, would be integrated and proved to work, safely, as part of the whole a/c before being signed off to the customer. What you need to ask, though, is how do you define, and prove, "works". If you have lots of time and money you can go and fire real missiles and see if it detects them, if you've integrated some reaponse, eg jammer, chaff, flares, you can test those at the same time. If you haven't got enough dosh to pay for that, then you need to start making a compromise and that is were the bigboys and their advisers have to stand up and be counted because everything that isn't tested becomes a risk which the head honcho of an IPT has to sign for as a risk he's willing to take - or rather he's willing to let you take. Now, you could use a missile simulator but you take the risk that it is a good representation of all the missiles the system is designed to detect. Of course all this can only be done in a peacetime environment, no-one can be expected to contract that it will work just the same in a war - for a start you can't count on the enemy to use exactly what you specified as the threat. What you can prve is that the installation and integration is safe from an operator point of view e.g when you turn it on the bombs don't go off due to EMC, but you can never "prove" safety in an operational i.e wartime environment
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If I am asked to procure say, a Missile Approach Warner, what on earth is the point of bolting it into the aircraft and then, along with the contractor, being allowed to walk away without integrating it and proving that it works, safely, as part of the whole aircraft? But, because a MAW (hopefully) is not required during peacetime ops, that's precisely what is permitted. It doesn't always happen, because some of us ignore the "rules" and make it safe.
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