A rubber screwdriver when tested using a conduction test

A metallic pin when tested using a conduction test

Sometimes a bulb doesn't light up because

Sometimes a circuit despite complete doesn't work because

A clip when tested using a coduction test

will not light the bulb

will light up the bulb

the bulb is fused.

the cells are not arranged properly

may or may not light up the bulb depending on the nature of its material.