input: Write a python function to list the files in the current directory using subprocess.
  assert set(list_files()) == set(subprocess.run(['ls'], stdout=subprocess.PIPE, universal_newlines=True).stdout.splitlines())
  assert isinstance(list_files(), list)
  assert all(isinstance(f, str) for f in list_files())
output: def list_files():
      import subprocess
      result = subprocess.run(['ls'], stdout=subprocess.PIPE, universal_newlines=True)
      return result.stdout.splitlines()