code: def test_default_wall_time(self):
      output = mock.create_autospec(output_lib.Output)
      w = writer_lib.Writer(output)
      with mock.patch.object(time, "time") as mock_time:
          mock_time.return_value = 12345.678
          w.add_scalar("foo", 42.0, 12)
      output.emit_scalar.assert_called_once()
      _, kwargs = output.emit_scalar.call_args
      self.assertEqual(12345.678, kwargs["wall_time"])
  
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 6 for calling the WriterAddScalarTest obj's underlying member method code with example usage: obj.test_default_wall_time() without return types