'Test that a 3x3x3 unit kernel returns the same array (except when
boundary is None).'

@pytest.mark.parametrize(u'boundary', BOUNDARY_OPTIONS)
def test_unity_3x3x3(self, boundary):

    x = np.array([[[1.0, 2.0, 1.0], [2.0, 3.0, 1.0], [3.0, 2.0, 5.0]], [[4.0, 3.0, 1.0], [5.0, 3.0, 2.0], [6.0, 1.0, 1.0]], [[7.0, 0.0, 2.0], [8.0, 2.0, 3.0], [9.0, 2.0, 2.0]]], dtype=u'>f8')
    y = np.zeros((3, 3, 3), dtype=u'>f8')
    y[(1, 1, 1)] = 1.0
    z = convolve(x, y, boundary=boundary)
    if (boundary is None):
        assert np.all((z == np.array([[[0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0]], [[0.0, 0.0, 0.0], [0.0, 3.0, 0.0], [0.0, 0.0, 0.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]], dtype=u'>f8')))
    else:
        assert np.all((z == x))
