>>> from students import students_per_subject

>>> dic = {('Pol','Amber','Coll'):['PHY','PE','CHM'],
... ('Aina','Soler','Gil'):['PHY','PE','CHM','MTH'],
... ('Joan','Rubio','Boix'):['PE','CHM','MTH', 'ENG'],
... ('Mar','Pou','Coll'):['PE','GE']}
>>> ds = students_per_subject(dic)
>>> if ds != {'PHY':2,'PE':4,'CHM':3,'MTH':2,'ENG':1,'GE':1}:
...     print(ds)