input: from typing import List
  
  
  def substring_in_order(string: str) -> List[str]:
      """Given a string, this function returns a list of all its substrings in order from longest to shortest.
      
      >>> substring_in_order('abc')
      ['abc', 'ab', 'bc', 'a', 'b', 'c']
      >>> substring_in_order('testing')
      ['testing', 'testin', 'esting', 'testi', 'test', 'esti', 'test', 'ting', 'tin', 'est', 'test', 'ting', 'tin', 'ing', 'est', 'ti', 'te', 'test', 't', 'e', 's', 't', 'i', 'n', 'g']
      """
      result = [] 
      n = len(string) 
      for l in range(n, 0, -1): 
          for i in range(n-l + 1): 
              result.append(string[i:i+l]) 
      return result
output:     result = [] 
      n = len(string) 
      for l in range(n, 0, -1): 
          for i in range(n-l + 1): 
              result.append(string[i:i+l]) 
      return result