def compas_quadmesh_to_occ_shell(mesh: Mesh) -> TopoDS_Shell:
"""Convert a COMPAS quad mesh to an OCC shell.
Parameters
----------
mesh : :class:`~compas.datastructures.Mesh`
A COMPAS mesh data structure with quad faces.
Returns
-------
TopoDS_Shell
Raises
------
AssertionError
If the input mesh is not a quad mesh.
"""
assert mesh.is_quadmesh(), "The input mesh is not a quad mesh."
shell = TopoDS_Shell()
builder = BRep_Builder()
builder.MakeShell(shell)
for face in mesh.faces():
points = mesh.face_coordinates(face)
builder.Add(shell, quad_to_face(points))
return shell
