How to tell if a cd player is bad?

ok to make a long story short i was installing a used cd player in my friend's car, it was her sisters cd player and she said it worked fine for her but some lights and stuff were broke.

Anyways there was already an aftermarket cassette player, the previous owners did some kid of wierd makeshift harness, i disconnected their wires and put mine on same color but didnt work. SO my next idea was to just use the wire diagram and hook it up directly to the car, cd player still didnt work. Now i hook the cassette player up to the ignition, ground, battery and it worked... now the fuse on the cd player looks fine but are there any ways to check to see if it works at all because it supposedly did before? 

thanks, probably a stupid questions but it seems like a waste to buy a new one.

ok, well i think its bad because the cassette player worked and i just connect its wires to the already connected cd player wires.

For the ground i just used the black wire, i figured this was alright.

As for taking it back, its my friends and i'm helping install it in her car so the only thing i lost was wiring time.

also i dont want to start a new topic for this question because i think its a little dumb but would it be possible to take out your car's factory unit and just replace it with a Diskman(portable cd player). I understand the sound and everything would be bad but you could power it through the lighter or even set up some resistors and power it from the wires.

Ofcourse this would just be for novelty purposes but is is do-able with atleast decent sound?

thanks 

Well uisgdlysat, I recommend geting new cd player, Sometimes you can get away with a used one, Theres no doubt. For me I preffer a full working cd player I dont like things work %50. I guess I am just picky. In the long run its money worth spent, Then you can enjoy youre music without hassels.

Good Luck.