input: Write a class to modify the case of the string. Implement methods to convert the string to uppercase, lowercase, and title case.
  
  class StringCaseModifier:
      def __init__(self, string):
          self.string = string
  
      def to_upper(self):
          return self.string.upper()
  
      def to_lower(self):
          return self.string.lower()
      
      def to_title(self):
          return self.string.title()
  
  if __name__ == '__main__':
      test_string = 'Hello World'
      string_modifier = StringCaseModifier(test_string)
      assert string_modifier.to_upper() == 'HELLO WORLD'
      assert string_modifier.to_lower() == 'hello world'
      assert string_modifier.to_title() == 'Hello World'
output: class StringCaseModifier:
      def __init__(self, string):
          self.string = string
  
      def to_upper(self):
          return self.string.upper()
  
      def to_lower(self):
          return self.string.lower()
      
      def to_title(self):
          return self.string.title()