Hi,
The interrupt can be triggered on either the rising or falling edge of the signal connected to PortB.0 (ie the interrupt fires when the signal changes state). You select rising/falling edge by setting or clearing OPTION_REG.6

If, during normal operation, the signal connected to PortB.0 is high and it goes low when there's a problem you want to set it up so it interrupts on the falling edge. (OPTION_REG.6 = 0)

Yes, to test it, pull up PortB.0 with a resistor and use a switch/button/whatever to pull it low and trig the interrupt. Note that you are likely to get some contact bounce with a mecanical switch/button which may trig the interrupt several time for each press of the button.