If you're using Linux, I would recommend using TemporaryFile instead of NamedTemporaryFile. It takes advantage of the O_TMPFILE flag, which guarantees that the kernel will clean up the file for you when the process exits:

  import shutil
  import tempfile

  @pytest.fixture
  def libfact():
      tmp = tempfile.TemporaryFile()
      tmp_name = f"/dev/fd/{tmp.name}"
      shutil.copy2("./fact.so", tmp_name)
      lib = CDLL(tmp_name)
      yield lib

It's better than relying on your application to clean up the file for you. With application-level cleanup hooks, you're still vulnerable to a resource leak if the process gets a SIGKILL or crashes or otherwise ends before your hooks run.