code: def test_addition(self):
      p = ggplot(data, aes("x", "y"))
      p1 = p + self.lyrs[0] + self.lyrs[1] + self.lyrs[2]
      assert _get_colors(p1) == colors
  
      p2 = p + self.lyrs
      assert _get_colors(p2) == colors
  
      # Real layers
      lyrs = Layers(layer.from_geom(obj) for obj in self.lyrs)
      p3 = p + lyrs
      assert _get_colors(p3) == colors
  
      p += self.lyrs
      assert _get_colors(p) == colors
  
      with pytest.raises(PlotnineError):
          geom_point() + layer.from_geom(geom_point())
  
      with pytest.raises(PlotnineError):
          geom_point() + self.lyrs
  
file_path: plotnine/tests/test_layers.py
imports: from pathlib import Path
  import numpy
  import pandas
  import pytest
  from plotnine import aes, geom_path, geom_point, ggplot
  from plotnine.exceptions import PlotnineError, PlotnineWarning
  from plotnine.layer import Layers, layer
label_desc: Use image node_id 1 for calling the TestLayers obj's underlying member method code with example usage: obj.test_addition() without return types