  We compare two different tests of quantum non-locality, both in theoretical
terms and with respect to a possible implementation in a mesoscopic circuit:
Hardy's test [Hardy, Phys. Rev. Lett. \textbf{68}, 2981 (1992)] and the CHSH
test, the latter including a recently discovered inequality relevant for
experiments with three possible outcomes [Collins and Gisin, J. Phys. A
\textbf{37}, 1775 (2004)]. We clarify the geometry of the correlations defined
by Hardy's equations with respect to the polytope of causal correlations, and
show that these equations generalize to the CHSH inequality if the slightest
imperfections in the setup need to be taken into account. We propose a
mesoscopic circuit consisting of two interacting Mach-Zehnder interferometers
in a Hall bar system for which both Hardy's test and the CHSH test can be
realized with a simple change of gate voltages, and evaluate the robustness of
the two tests in the case of fluctuating experimental parameters. The proposed
setup is remarkably robust and should work for fluctuations of beam splitter
angles or phases up to the order of one radian, or single particle loss rates
up to about 15%.
