old_contents: __all__ = ['nfw',
             'mass_concentration',
             ]
  
  from .nfw import NFW
  from . import mass_concentration
  
  
new_contents: __all__ = ['nfw',
             'mass_concentration',
             ]
  
  from .nfw import NFW
  from . import mass_concentration
  
  from numpy.testing import Tester
  test = Tester().test
  
  
subject: add module test method