a simple circuit (thing)

bob the cow is wrong because every medium across which voltage can be induced has some resistance, even if it is infintesimal. Remember: V=iR, by definition.

baffo is wrong because the mechanism to change the magnetic field can be modelled as a voltage source, reducing it to StormHunter's example.

StormHunter's example is correct for almost every instance you can see in The Real World, but one can induce a current in a loop of superconducting material, then remove the transient and let it run indefinitely, or until you perturb its magnetic field. R=0, so V=0.

    i -->
/-------------\
|             |
|             |
\_____________/