Write a python function to convert the given string to lower case.
def is_lower(string):
  return (string.lower())
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a python function to convert the given string to lower case.
def is_lower(string):
  return (string.lower())[/INST]assert is_lower("InValid") == "invalid"
assert is_lower("TruE") == "true"
assert is_lower("SenTenCE") == "sentence"</s>