to test a conductor with superconductive material which is in the superconducting state , the conductor is led through an external magnetic field which comprises at least two magnetic field regions spatially separated from each other and arranged one behind the other in the lengthwise direction of the conductor , the fields of which are angularly displaced from each other in the circumferential direction relative to the longitudinal axis of the conductor permitting disturbances in all superconductivity regions in superconductors of any cross section to be ascertained with certainty .