  We consider an integrability test for ultradiscrete equations based on the
singularity confinement analysis for discrete equations. We show how
singularity pattern of the test is transformed into that of ultradiscrete
equation. The ultradiscrete solution pattern can be interpreted as a perturbed
solution. We can also check an integrability of a given equation by a
perturbation growth of a solution, namely Lyapunov exponent. Therefore,
singularity confinement test and Lyapunov exponent are related each other in
ultradiscrete equations and we propose an integrability test from this point of
view.
