In the context of testing the specification of a nonlinear
parametric regression function, we adopt a nonparametric minimax
approach to determine the maximum rate at which a set of smooth
alternatives can approach the null hypothesis while ensuring
that a test can uniformly detect any alternative in this set
with some predetermined power. We show that a smooth nonparametric
test has optimal asymptotic minimax properties for regular
alternatives. As a by-product, we obtain the rate of the smoothing
parameter that ensures rate-optimality of the test. We show
that, in contrast, a class of nonsmooth tests, which includes
the integrated conditional moment test of Bierens (1982,
Journal of Econometrics 20, 105–134), has suboptimal
asymptotic minimax properties.