There is a backlight testing tool that bypasses the inverter so you can test the bulb in the screen (found on eBay less that $15 US - usually ships from China/HongKong - Search "CCFL Tester").
Testing the inverter is not so easy. Your best bet is to rule out the cheapest solutions first. Instead of the tester, you can find an inverter for about the same cost (also on eBay - Search "P300 inverter").
A local computer repair shop should have all these things available to make quick work of it

I'm not talking about BestBuy, look for a locally owned shop.
*ALWAYS* Remove all power sources (wall power/battery) and drain residual power by holding down the power button before doing any work, or you can easily do more $$$ damage.