test_comp_surface_rotor
Check that the computation of the surface is correct
test_comp_surface_stator
test_comp_volume_rotor
Check that the computation of the volume is correct
test_comp_volume_stator
test_comp_mass
Check that the computation of the mass is correct
test_comp_mass_shaft_none
Check that the compytation of the mass is correct even if there is no shaft