If the car is in gear not Park or Neutaral the PNP switch will stop the engine cranking not the fuel injectors firing. And if it is gear and the switch not fitted properly I image you'll hear the engine load up while cranking or try to slightly move the car . If its in gear best re check it or leave the drive shafts out while you test.
Noid lights are simple cheap and easy for checking fuel injectors. I use this exact set professionally for years and I can't fault them.
Its also handy to have a fuel pressure tester that has a coupling to suit the volvo fuel rail I have this one and it has the right angle fitted that easily screw onto the fuel rail.
A few hundred dollars in simple tools will make diagnosing your volvo in the future far more easier or any car really..
Toledo Noid Light and Iac Signal Test Set - 307226 - Toledo | Repco Australia https://www.repco.com.au/en/tools-equipment/automotive-tools/electrical/toledo-noid-light-and-iac-signal-test-set-307226/p/A9305252
Fuel pressure tester to suit volvo 850
https://au.jbtools.com/cta-tools-3448-volvo-fuel-rail-test-kit-pressure-tester/
If injectors arnt firing i would be first checking all fuses and plugs then crank angle sensor and possibly cam angle. More thank likely cam angle will cause a slow to start situation eg cranks for a long period then fires.
Its always good to check the fault codes also just to see what's going on.