code: def test_add_trace(self):
      # Add a trace
      self.figure.add_trace(go.Sankey(arrangement="snap"))
  
      # Check access properties
      self.assertEqual(self.figure.data[-1].type, "sankey")
      self.assertEqual(self.figure.data[-1].arrangement, "snap")
  
      # Check message
      self.figure._send_addTraces_msg.assert_called_once_with(
          [{"type": "sankey", "arrangement": "snap"}]
      )
  
file_path: plotly.py/packages/python/plotly/plotly/tests/test_core/test_figure_messages/test_add_traces.py
imports: import sys
  from unittest import TestCase
  import plotly.graph_objs
  from plotly.subplots import make_subplots
label_desc: Use image node_id 2 for calling the TestAddTracesMessage obj's underlying member method code with example usage: obj.test_add_trace() without return types