input: Write a class to modify the case of a given string. The class should have methods to convert the string to uppercase, lowercase, and title case. If the input string is "Hello World", the output should be "HELLO WORLD", "hello world", and "Hello World" respectively.
  
  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()