  The accurate modeling of electromagnetic penetration is an important topic in
computational electromagnetics. Electromagnetic penetration occurs through
intentional or inadvertent openings in an enclosed electromagnetic scatterer,
which prevent the contents from being fully shielded from external fields. To
efficiently model electromagnetic penetration, aperture or slot models can be
used with surface integral equations to solve Maxwell's equations. A necessary
step towards establishing the credibility of these models is to assess the
correctness of the implementation of the underlying numerical methods through
code verification. Surface integral equations and slot models yield multiple
interacting sources of numerical error and other challenges, which render
traditional code-verification approaches ineffective. In this paper, we provide
approaches to separately measure the numerical errors arising from these
different error sources for the method-of-moments implementation of the
electric-field integral equation with a slot model. We demonstrate the
effectiveness of these approaches for a variety of cases.
