  We test a theoretical description of the void size distribution function
against direct estimates from halo catalogues of the DEMNUni suite of large
cosmological simulations. Besides standard $\Lambda$CDM, we consider deviations
of the dark energy equation of state from $w=-1$, corresponding to four
combinations in the popular Chevallier-Polarski-Linder parametrisation:
$w_0=-0.9;-1.1$, $w_a=-0.3;0.3$. The theoretical void size function model,
relying on the Sheth & van de Weygaert double barrier excursion set formalism,
provides an accurate description of the simulation measurements for the
different dark energy models considered, within the statistical errors. The
model remains accurate for any value of the threshold for void formation
$\delta_\mathrm{v}$. Its robust consistency with simulations demonstrates that
the theoretical void size function can be applied to real data as a sensitive
tool to constrain dark energy.
