I did a leak test on my RV-12iS fuel system after all of the main lines were in but before the engine arrived. So, no engine and no fuel pumps. So, none of the fuel pump and fuel filter fuel interconnect lines were installed.
I capped the fuel supply line that connects to the main filter at the filter end. I removed the fuel tank and capped the fuel return line that connects to the tank. At the firewall I capped one line and placed a pressure gauge with a tire valve to the other. I was then able to pressurize the system and check for leaks. The fuel supply and return lines are connected through a small orifice in the bypass fitting so both sides of the system, supply and return, can now be pressurized.
Yes, I found some leaks. I was able to trouble shoot using a spray bottle with soapy water. I would pressurize and then if the pressure had dropped I checked for bubbles at the fittings. At the end the system held 55 psi for several days. I figured that even though this did not test the entire system it did test lines and fittings that will be very difficult to work on after the controls, engine and avionics are installed.
Later, after the pumps were installed I performed a similar test of the system with those lines installed. Again, without the tank.
I'm not sure if the pumps will pressurize a dry system. I don't want to run my pumps dry in any event. After installation of the pumps and avionics/electrical system I turned each on for a second or two just to verify the wiring and connections. I don't plan to run them again until there is fuel in the system.
Henry