input: Write a python function to create a root directory with two child directories. 
  assert create_directories() == ["root/child_dir_1", "root/child_dir_2"]
  assert os.path.exists("root/child_dir_1") == True
  assert os.path.exists("root/child_dir_2") == True
output: def create_directories():
      import os
      
      root_dir = "root"
      child_dir_1 = os.path.join(root_dir, "child_dir_1")
      child_dir_2 = os.path.join(root_dir, "child_dir_2")
      
      os.makedirs(child_dir_1, exist_ok=True)
      os.makedirs(child_dir_2, exist_ok=True)
      
      return [child_dir_1, child_dir_2]