Here is my homemade pop tester made from parts I bought used on ebay (like a portapower), a 3000psi guage, an injector line for free from a junkyard, and a clear salsa jar it sprays into:
Its a hand hydraulic pump that can do 4000psi, some have used 2 ton bottle jacks for this, but that requires welding, and epoxy, and is subject to leaks which could be dangerous (due to injection of high pressure diesel under the skin.) Mine was easy to build, no leaks and pumps easily, and required only a few plumbing fittings shown in the picture, since it already had a pipe threaded inlet and outlet on the pump. This pump has a knob you can see on the right end of the pump which releases the pressure, making it safer when you unscrew the injector. I got the portapower type pump (power team P23) barely used on ebay, for $67, and I have seen several like it on ebay sell for $40-60. Then I added these parts from mcmaster:
5269K311 METRIC STEEL COMPRESSION TUBE FITTING, ADAPTER FOR 6 MM TUBE OD X 1/8" NPT MALE PIPE 3.47
50925K343 COMPACT EXTREME-PRESSURE STEEL THRD FITTING, 3/8"MALE X 1/8"FEM PIPE, HEX HEAD BUSHING,6000 PSI 1.53
3845K23 GLYCERIN-FILLED GAUGE - 1% MID-SCALE ACCURACY, 2-1/2" DIAL, 1/4" BOTTOM, 0 - 3000 PSI 18.49
50925K345 COMPACT EXTREME-PRESSURE STEEL THRD FITTING, 3/8"MALE X 1/4"FEM PIPE,HEX HEAD BUSHING, 6000 PSI 1.30
50925K198 COMPACT EXTREME-PRESSURE STEEL THRD FITTING, 3/8" PIPE, FEMALE X FEMALE X MALE TEE, 4500 PSI 7.11
Here is a thread where I discuss using the pop tester for my new nozzles:
Monark vs. Bosio nozzles
I highly recommend getting your injectors pop tested, it made a big difference for me.