def test_subdim_fd(self):
        """
        Test that the FD shortcuts are handled correctly with SubDimensions
        """
        grid = Grid(shape=(20, 20))
        x, y = grid.dimensions

        u = TimeFunction(name='u', save=None, grid=grid, space_order=1, time_order=1)
        u.data[:] = 2.

        # Flows inward (i.e. forward) rather than outward
        eq = [Eq(u.forward, u.dx + u.dy, subdomain=grid.interior)]

        op = Operator(eq)

        op.apply(time_M=0)

        assert np.all(u.data[1, -1, :] == 2.)
        assert np.all(u.data[1, :, 0] == 2.)
        assert np.all(u.data[1, :, -1] == 2.)
        assert np.all(u.data[1, 0, :] == 2.)
        assert np.all(u.data[1, 1:18, 1:18] == 0.)