Hmmm, sorry. Adding fuel is not needed, it should have read BEFORE ADDING FUEL.
But just to be sure we are on the same page : I assumed you were going to test for the following:
Verify:
1. Purge the fuel lines so clean fuel comes out, nothing is plugged.
2. that the fuel system does not leak, suction or pressure side
3. that the boost pump will deliver full fuel flow (in case of a mechanical pump failure) at the needed pressure for full power/full rich take off.
4. quantify each tank for usable fuel under full flow at pressure conditions
Meaning,
run a leak test before fuel is introduced to the system,
then tilt the plane,
put a measured amount of fuel in each tank,
activate the pump and purge until it flows clear measure and discard that fuel.
activate the fuel pump, read pressure and flow from the panel and adjust back pressure with the exit flow valve.
Then once the fuel pressure drops (tone of the pump changes when it gets air) shut off the valve and measure fuel pumped out.
The test is rerun for as much nose down as you can safely do. A landing phase angle.
Actually, on a 10 the pressure does not drop until something less than a quart remains with the nose up. There is a bit more unusable fuel nose down but not gallons.
Is that more descriptive of what you want to accomplish, or are you running a test for a different purpose?