Well I'd like to know how the alternator was tested. To test it you have to run it at idle speed and load it up so that it delivers maximum wattage out. I think this car has a 700-900 Watt alternator. That means about 50-60 Amps of current load. Is this what your friend did?
If the alternator is new or rebuilt its seems reasonable it should work (not always but lets take it as a starting point). If the alternator is good, the belt is good, and the engine running, then the problem is getting the energy back to the battery. Do you have loose or corroded wires from the alternator to the battery? Is the ground wire from the battery loose or corroded at either end (battery and chassis ends). To allow 60 amps of current to flow this needs to be a very tight and clean connections.
Using a DVM measure the battery voltage at its + and - terminals with engine switched off. Should be around 12 VDC. Then start up car and let it idle with everything electrical switched off you can turn off. The voltage across the + and - terminals should be around 13.3 VDC. If you are still around 12VDC or less then you have no recharge at all suggesting faulty alternator or really bad or disconnected wires. If you have 13.3 VDC then start turning on everything electrical, high beams, bun warmers, AC blower fan, rear window defrost, ... Now measure battery voltage. If it is below 13.3 volts it shows the alternator is not charging enough to keep up with the load. Maybe bad alternator (worn brushes, bad regulator or a stator diode is fried). Since your alternator is new maybe not the case then it has to be the wiring. I am assuming here your battery is good since you said it was new.
If wiring is bad it will have a voltage drop across it. While engine runs and all electrical on measure voltage from battery - terminal to a bare metal on the engine block. Should be near zero volts. Anything above 0.5 VDC suggests a poor connection from battery to ground. Next is to measure voltage from charging terminal of alternator to the + terminal of the battery. This should be near zero as well. If higher then that link is a problem. Be careful on this last measurement. Set up measurement wires before you turn on car so you don't get injured. Also shorting wires from battery + to ground can be dangerous. Be careful.
