content: import pytest
  
  import pandas
  
  
  def test_matplotlib_backend_error():
      msg = ('matplotlib is required for plotting when the default backend '
             '"matplotlib" is selected.')
      try:
          import matplotlib  # noqa
      except ImportError:
          with pytest.raises(ImportError, match=msg):
              pandas.set_option('plotting.backend', 'matplotlib')
  
  
  def test_backend_is_not_module():
      msg = ('"not_an_existing_module" does not seem to be an installed module. '
             'A pandas plotting backend must be a module that can be imported')
      with pytest.raises(ValueError, match=msg):
          pandas.set_option('plotting.backend', 'not_an_existing_module')
  
  
  def test_backend_is_correct(monkeypatch):
      monkeypatch.setattr('pandas.core.config_init.importlib.import_module',
                          lambda name: None)
      pandas.set_option('plotting.backend', 'correct_backend')
      assert pandas.get_option('plotting.backend') == 'correct_backend'
  
      # Restore backend for other tests (matplotlib can be not installed)
      try:
          pandas.set_option('plotting.backend', 'matplotlib')
      except ImportError:
          pass
  