input: Write a function to determine if the sum of two integers can be calculated using the provided Python class 'Sum'. The class should be instantiated with two integers and should have an 'add' method that returns their sum.
  
  
  assert Sum(3, 4).add() == 7
  assert Sum(-1, 1).add() == 0
  
output: def can_sum_be_calculated(a, b):
      return Sum(a, b).add()