That's really more of a contractor type of question because it all depends on how extensive/deep it is/was. I do know that you can get cheapish test kits to see if there are any spores shedding into the living area.

Not the OP but my friend went through something similar with a bad rental. Step one is get a dehumidifier, deprive the mold of the moisture it needs. This won't solve the main problem, especially if the roof is leaking, but it'll help keep mold off of interior surfaces like walls. Step two: bleach works to kill the mold, but does nothing for further prevention. What we used was foaming mold killer spray. It clings to the walls and also will prevent mold from coming back. And please, please get a checkup from a doctor once you have moved out. My friend had a lot of inflammation and other problems from living with the mold for so long. Dr was able to manage her recovery and help her to get back on track. Also fuck your landlord they sound like a real peice of work.