old_contents: """Tests for ``xentica.core.renderers`` module."""
  import unittest
  
  from xentica.core.renderers import Renderer
  
  
  class TestRenderer(unittest.TestCase):
      """Tests for ``Renderer`` class."""
  
      def test_base(self):
          """Test base class is returning empty code for kernel."""
          renderer = Renderer()
          code = renderer.render_code()
          self.assertEqual(code, "", "Base class kernel should be empty")
  
new_contents: """Tests for ``xentica.core.renderers`` module."""
  import unittest
  
  from xentica.core.renderers import Renderer, RendererPlain
  
  
  class TestRenderer(unittest.TestCase):
      """Tests for ``Renderer`` class."""
  
      def test_base(self):
          """Test base class is returning empty code for kernel."""
          renderer = Renderer()
          code = renderer.render_code()
          self.assertEqual(code, "", "Base class kernel should be empty")
  
      def test_renderer_plain(self):
          """Test ``RendererPlain`` class."""
          renderer = RendererPlain(projection_axes=(1, 0))
          self.assertEqual(renderer.projection_axes, (1, 0), "Wrong axis")
  
subject: Add test for RendererPlain class (#40)