"Also, in reading some of the posts I am leaning to the conclusion that a fire pump downstream of the DCVA makes the forward flow test un-necessary?"
This is correct.
A pump test requires 150% of rated capacity and you can not design a system that exceeds 150% rated capacity of the fire pump.
I would guess a 2" main drain would be fine on a lot of light hazard systems. Not all but a lot of them especially if the designer used the quick response/low ceiling reduction for the ara of application.
On Ordinary Hazard Occupancies *some* might be OK with a 2" main drain but I would guess most city water supply systems would fail to deliver the required flow. For ordinary hazard occupancies it wouldn't be that big of a deal to reverse the fire department check valve and use the 4" FDC to achieve the flow.
On most high piled storage/extra hazard occupancy systems the 4" might not be able to deliver the required water supply and I can see something similar to a fire pump test header or a straight pipe larger then 6" discharging outside the building.
On larger systems you might find a fire hydrant downstream the fire pump and you can always use that.
I suppose you can always run a 4" or 6" main drain too. Not a huge deal just a butterfly valve, little bit of pipe and couple elbows.
In Georgia I have yet to be anywhere this is pushed. In South Carolina an actual pump test header assembly is required.
