input: Write a function to list the contents of a directory. Return the list of contents as a Python list. If the directory is empty, return an empty list.
  list_directory_contents()
  assert list_directory_contents()==[]
  assert list_directory_contents()==["file1.txt", "file2.txt", "folder"]
output: 
  def list_directory_contents():
      import os
      return os.listdir()
  