A testing apparatus includes a first power supply unit and first and second coaxial cables. The first power supply supplies current to a device under test. The first coaxial cable includes a first internal conductor and a first external conductor. The second coaxial cable includes a second internal conductor and a second external conductor. The first internal conductor and the second external conductor conducts current from the first power supply unit to the device under test. The second internal conductor and the first external conductor conducts current from the device under test to the first power supply unit.