xpass NURBS Curve derivatives, as these are currently broken but don't fail

Author: cshorler

tests/test_curve.py

@@ -279,6 +279,9 @@ def test_nurbs_curve2d_slice_eval(unit_circle_tri_ctrlpts, param, res):
     assert abs(evalpt[0] - res[0]) < GEOMDL_DELTA
     assert abs(evalpt[1] - res[1]) < GEOMDL_DELTA
 
+
+# TODO: derivative of a circle is a circle
+@mark.xfail
 @mark.parametrize("param, order, res", [
     (0.0, 1, ((5.0, 5.0), (90.9090, 90.9090))),
     (0.2, 2, ((13.8181, 11.5103), (40.0602, 17.3878), (104.4062, -29.3672))),