input: Write a function that checks if a given string contains all words from a given list of words. The function should return True if the string contains all the words; otherwise, it should return False.
  
  def contains_words(input_string, words):
   for word in words:
   if word not in input_string:
   return False
   return True
  
  assert contains_words('This is a test', ['test', 'this', 'is'])==True
  assert contains_words('Hello world', ['world', 'hello'])==False
  assert contains_words('Python is fun', ['Python', 'fun'])==True
  assert contains_words('Testing out functions', ['test', 'function'])==False
  assert contains_words('', [''])==False
output: def contains_words(input_string, words):
      input_string = input_string.lower()
      for word in words:
          if word.lower() not in input_string:
              return False
      return True