code: def test_volume_mapper_blend_mode(volume_mapper, skip_check_gc):
      assert isinstance(volume_mapper.blend_mode, str)
  
      volume_mapper.blend_mode = vtk.vtkVolumeMapper.COMPOSITE_BLEND
      assert volume_mapper.blend_mode == "composite"
  
      for mode in [
          "average",
          "minimum",
          "maximum",
          "composite",
          "additive",
      ]:
          volume_mapper.blend_mode = mode
          assert volume_mapper.blend_mode == mode
  
      with pytest.raises(
          ValueError, match='Please choose either "additive"'
      ):
          volume_mapper.blend_mode = "not a mode"
  
      with pytest.raises(TypeError, match="int or str"):
          volume_mapper.blend_mode = 0.5
  
imports: import pytest
  import vtk
  import pyvista
label_desc: Use image node_id 3 for calling a global function with example usage: test_volume_mapper_blend_mode(volume_mapper, skip_check_gc) without return types