Unittest to ensure that the macro ALLOW_BACKPROP works correctly.
The test instrument includes two monitors, with a selectable ALLOW_BACKPROP in between.
The second monitor is placed physically "earlier" than the first, but logically after.
1) With Backprop=0 the second monitor (closer to the source) should yield a signal of 0
2) With Backprop=1 the second monitor should measure a signal since backpropagation is allowed
Input parameters
Parameters in boldface are required;
the others are optional.