Any reasonable testing requires an oscilloscope: See http://www.camrystuff.com/manuals/Gen4/Diagnostics.pdf page 283.
You can also check for a short between the output and ground (it's a piezo sensor, so can't really check for an open -- they always look like an open at DC), and, although the FSM doesn't mention it, you should be able to use a multimeter on a fairly sensitive scale (peak output is well under a volt) to compare the output of the two sensors when the engine is rockin' and rollin'.
You can also check for a short between the output and ground (it's a piezo sensor, so can't really check for an open -- they always look like an open at DC), and, although the FSM doesn't mention it, you should be able to use a multimeter on a fairly sensitive scale (peak output is well under a volt) to compare the output of the two sensors when the engine is rockin' and rollin'.