input: Write a function to convert a given string to a list of integers. The function should split the string by commas and then convert each split part to an integer.
  
  def to_int_list(s):
      return [int(x) for x in s.split(',')]
  
  assert to_int_list('1,2,3,4,5')==[1, 2, 3, 4, 5]
  assert to_int_list('10,20,30')==[10, 20, 30]
  assert to_int_list('5,10,15,20')==[5, 10, 15, 20]
  assert to_int_list('100,200,300')==[100, 200, 300]
  assert to_int_list('')==[]
output: def to_int_list(s):
      return [int(x) for x in s.split(',')]