<human>:  With regards to superconductivity and Josephson junctions, how do you know that a superconductor is superconducting?
<bot>: You can test for superconductivity using a Josephson junction. A Josephson junction is a device that consists of two superconductors separated by a thin insulator. If the insulator is thin enough, electrons can tunnel through the insulator and the junction will act as a switch, with current flowing only when the voltage is applied.