  The abundance of cosmic voids can be described by an analogue of halo mass
functions for galaxy clusters. In this work, we explore a number of void mass
functions: from those based on excursion-set theory to new mass functions
obtained by modifying halo mass functions. We show how different void mass
functions vary in their predictions for the largest void expected in an
observational volume, and compare those predictions to observational data. Our
extreme-value formalism is shown to be a new practical tool for testing void
theories against simulation and observation.
