input: Write a function that takes any number of integer arguments and returns their sum. The function should be named `sum_ints` and should accept a variable number of arguments using `*args`. Each argument should be added to the total sum, which should then be returned. If no arguments are provided, the function should return 0. Provide test cases to verify the function with various inputs.
  
  assert sum_ints(3, 5, 7) == 15
  assert sum_ints(1, 2, 3, 4, 5) == 15
  assert sum_ints(-1, 1) == 0
  assert sum_ints() == 0
output: def sum_ints(*args):
      return sum(args)