code: def test_flush_after_close(self):
      output = mock.create_autospec(output_lib.Output)
      w = writer_lib.Writer(output)
      w.close()
      with self.assertRaisesRegex(RuntimeError, "already closed"):
          w.flush()
  
imports: import time
  from unittest import mock
  import numpy
  from tensorboard.compat.proto import summary_pb2
  from tensorboard.summary import _output
  from tensorboard.summary import _writer
  from tensorboard.summary import _test_util
  from tensorboard.util import tensor_util
  from tensorboard import test
label_desc: Use image node_id 3 for calling the WriterTest obj's underlying member method code with example usage: obj.test_flush_after_close() without return types