input: Write a python function to check if one string is a rotation of another.
  assert is_rotation("ABACD", "CDABA") == True
  assert is_rotation("ABACD", "ACDAB") == True
  assert is_rotation("ABACD", "DABAC") == True
  assert is_rotation("ABACD", "ABACD") == True
  assert is_rotation("ABACD", "ABCDE") == False
  assert is_rotation("ABACD", "BACDA") == True
  assert is_rotation("ABACD", "BCDAA") == False
output: def is_rotation(s1, s2):
      if len(s1) != len(s2):
          return False
      return s2 in (s1 + s1)