Go to Home Depot or any hardware store and get the closest sized PVC piping that will fit into your hoses/couplers. get different end caps/plugs. Go to a gas station and ask them for a valve stem (they will probably just give you one, otherwise they are only like $1-2) drill a hole in one of the end caps and pull the valve stem through. Then just clamp the plugs to either end of the intercooler and fill it with air. You'll hear it leak if there is a hole, or just to be sure spray it w/ soapy water.
You can also thread a fitting in and attach a pressure gauge.
BE CAREFULL the pvc will slip out under too much pressure and shoot across the garage. I've never had one stay in much past 15 psi.