  Gravitational-wave data analysis requires a detailed understanding of the
highly relativistic, late stages of inspiral of neutron-star and black-hole
binaries. A promising method to compute the late inspiral and its emitted waves
is numerical relativity in co-rotating coordinates. The coordinates must be
kept co-rotating via an appropriate choice of numerical relativity's lapse and
shift functions. This article proposes a model problem for testing the ability
of various lapse and shift prescriptions to keep the coordinates co-rotating.
