i've played with this. you need about 30psi of pressure and a liquid with similar physical properties as gasoline to properly test the spray pattern. in my limited understanding of fluid dynamics i found that among the solvent i have access to, methanol has the closest viscosity to gasoline. so that's what i'm using. i figure you can probably dilute some isopropanol too.

to pressurize the liquid, you can hook up an injector to a 3/8" fuel hose, and hook the other end of the hose to a spare tire pumped to 30psi.

at this point you can at least tell if your injector is leaking.

then all you need to do is hooking up 12V to the injector. the poles are labeled on the injector itself. be careful not to ignite the spray!!