code: def test_only_one_value(Chart):
      """Test chart rendering with only one value"""
      chart = Chart()
      chart.add("S", [1])
      q = chart.render_pyquery()
      assert len(q(".legend")) == 1
  
imports: import io
  import os
  import uuid
  import pytest
  import pygal
  from pygal.graph.map import BaseMap
  from pygal.test import make_data
  from pygal.util import cut
label_desc: Use image node_id 7 for calling a global function with example usage: test_only_one_value(Chart) without return types