i am not familiar with a "fuse tester"... A fuse is metal connector of certain gauge and material that overheats if amperage over specific level passes through. nothin more, nothing less - a fuse is not a breaker or anything fancy, just a piece of wire.

if you have an OhmMeter (or a multimeter), all you have to do is test for continuity - if the fuse passes electricity, it is good, if the fuse does not pass electricity - it is not good.

So, i would suspect that you have a glorified OhmMeter... short the probes of the tester and see if the light comes on... it should... disengage the probes from each other - the light should extinguish...

same principle applies to the fuses - if the light is on, the fuse is good, if the light is not on, the fuse is not good...