input: Write a class to modify the case of the string.
  
  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()
  
  assert StringCaseModifier("Hello World").to_upper() == "HELLO WORLD"
  assert StringCaseModifier("Hello World").to_lower() == "hello world"
  assert StringCaseModifier("Hello World").to_title() == "Hello World"
  assert StringCaseModifier("hello world").to_upper() == "HELLO WORLD"
  assert StringCaseModifier("HELLO WORLD").to_lower() == "hello world"
  assert StringCaseModifier("hElLo WoRlD").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()