This test checks whether the swap coordinates protocol performs ion/water exchanges in z-direction.
The system is a typical computational electrophysiology setup with two octanol membranes in the x-y plane with
water and ions inbetween. At the start, there are 9 anions and 9 cations in one compartment (A) and 10 anions
and 10 cations in the other (B). The swap parameters are set such that all ions should end up in compartment A
in time step 2.
