void testFrontBack() {
    Model model("arm26.osim");
    const auto& state = model.initSystem();
    StatesTrajectory states;
    states.append(state);
    states.append(state);
    states.append(state);

    SimTK_TEST(&states.front() == &states[0]);
    SimTK_TEST(&states.back() == &states[2]);
}