code: def test_nagen():
      na = nagen()
      eq_(str(na), NA_STRING)
      eq_(repr(na), "nagen()")
      assert na.unknown is na
      assert na["unknown"] is na
  
      eq_(str(nagen("-")), "-")
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_nagen() without return types