I use the tester below that I thought I bought at Harbor Freight

Pittsburgh Fuel Injection Pump Tester #62623

Not sure they still carry this particular one...Although this model is available new and used on Ebay.

Be sure to use a little teflon tape where it screws to the fuel rail.

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'03 530i - manual swapped - 425k miles
'06 325Cic auto 115k
'05 X5 3.0 auto 158k
'99 E39 528i 5-speed 130k