input: Write a python function to test the functionality of the Lock class.
  assert lock_test() == True
  assert lock_test() == False
output: class Lock:
      def __init__(self):
          self.locked = False
  
      def lock(self):
          self.locked = True
  
      def unlock(self):
          self.locked = False
  
      def is_locked(self):
          return self.locked
  
  def lock_test():
      lock = Lock()
      lock.lock()
      if not lock.is_locked():
          return False
      lock.unlock()
      if lock.is_locked():
          return False
      return True