input: Write a function that converts a given string to a list of integers. The string input consists of integer values separated by commas. If the input string is empty, the function should return an empty list. If any part of the string cannot be converted to an integer, the function should raise a ValueError.
  
  def to_int_list(s):
      if not s:
          return []
      try:
          return [int(x) for x in s.split(',')]
      except ValueError:
          raise ValueError("Invalid input: parts of the string could not be converted to integers")
  
  assert to_int_list("1,2,3")==[1, 2, 3]
  assert to_int_list("4,0,-1")==[4, 0, -1]
  assert to_int_list("")==[]
  assert to_int_list("5,,6")  # should raise ValueError
  assert to_int_list("7,abc,8")  # should raise ValueError
  assert to_int_list("9")==[9]
  assert to_int_list("10,-11")==[10, -11]
  assert to_int_list("12,13,14,15")==[12, 13, 14, 15]
output: def to_int_list(s):
      if not s:
          return []
      try:
          return [int(x) for x in s.split(',')]
      except ValueError:
          raise ValueError("Invalid input: parts of the string could not be converted to integers")