  This manuscript presents verification cases that are developed to study the
electrothermal instability (ETI). Specific verification cases are included to
ensure that the unit physics components necessary to model the ETI are
accurate, providing a path for fluid-based codes to effectively simulate ETI in
the linear and nonlinear growth regimes. Two software frameworks with different
algorithmic approaches are compared for accuracy in their ability to simulate
diffusion of a magnetic field, linear growth of the ETI, and a fully nonlinear
ETI evolution. The nonlinear ETI simulations show early time agreement, with
some differences emerging, as noted in the wavenumber spectrum, late into the
nonlinear development of ETI. A sensitivity study explores the role of
equation-of-state (EOS), vacuum density, and vacuum resistivity. EOS and vacuum
resistivity are found to be the most critical factors in the modeling of
nonlinear ETI development.
