  It is generally accepted that the effective velocity of a viscous flow over a
porous bed satisfies the Beavers-Joseph slip law. To the contrary, interface
law for the effective stress has been a subject of controversy. Recently, a
pressure jump interface law has been rigorously derived by Marciniak-Czochra
and Mikeli\'c. In this paper, we provide a confirmation of the analytical
result using direct numerical simulation of the flow at the microscopic level.
