Conductive electronic device structures such as a conductive housing member that forms part of an antenna may be tested during manufacturing. A test system may be provided that has a capacitive coupling probe. The probe may have electrodes. The electrodes may be formed from patterned metal structures in a dielectric substrate. A test unit may provide radio-frequency test signals in a range of frequencies. The radio-frequency test signals may be applied to the conductive housing member or other conductive structures under test using the electrodes. Complex impedance data, forward transfer coefficient data, or other data may be used to determine whether the structures are faulty. A fixture may be used to hold the capacitive coupling probe in place against the conductive electronic device structures during testing.