input: Write a Python class to modify the case of a given string. The class should have three methods: `to_upper()`, `to_lower()`, and `to_title()`. The class should be initialized with a string, and each method should return the string modified to the respective 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)
      print(string_modifier.to_upper())
      print(string_modifier.to_lower())
      print(string_modifier.to_title())
  
  
  Assert test cases:
  
  
  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:
  - "HELLO WORLD"
  - "hello world"
  - "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()