  Colloidal systems are often modelled as fluids of hard particles (possibly
with an additional soft attraction, e.g. caused by polymers also contained in
the suspension). in simulations of such systems, the virial theorem cannot be
straightforwardly applied to obtain the components of the pressure tensor. In
systems confined by walls, it is hence also not straightforward to extract the
excess energy due to the wall (the "wall tension") from the pressure tensor
anisotropy. A comparative evaluation of several methods to circumvent this
problem is presented, using as examples fluids of hard spheres and the
Asakura-Oosawa model of colloid-polymer mixtures with a size ratio $q=0.15$
(for which the effect of the polymers can be integrated out to yield an
effective attractive potential between the colloids). Factors limiting the
accuracy of the various methods are carefully discussed, and controlling these
factors very good mutual agreement between the various methods is found.
