docs: def check_bounds_variables(self, dataset):
          '''
          Checks the grid boundary variables.
  
          :param netCDF4.Dataset dataset: An open netCDF dataset
          '''
          recommended_ctx = TestCtx(BaseCheck.MEDIUM, 'Recommended variables to describe grid boundaries')
  
          bounds_map = {
              'lat_bounds': {
                  'units': 'degrees_north',
                  'comment': 'latitude values at the north and south bounds of each pixel.'
              },
              'lon_bounds': {
                  'units': 'degrees_east',
                  'comment': 'longitude values at the west and east bounds of each pixel.'
              },
              'z_bounds': {
                  'comment': 'z bounds for each z value',
              },
              'time_bounds': {
                  'comment': 'time bounds for each time value'
              }
          }
  
          bounds_variables = [v.bounds for v in dataset.get_variables_by_attributes(bounds=lambda x: x is not None)]
  
          for variable in bounds_variables:
              ncvar = dataset.variables.get(variable, {})
              recommended_ctx.assert_true(ncvar != {}, 'a variable {} should exist as indicated by a bounds attribute'.format(variable))
              if ncvar == {}:
                  continue
  
              units = getattr(ncvar, 'units', '')
              if variable in bounds_map and 'units' in bounds_map[variable]:
                  recommended_ctx.assert_true(
                      units == bounds_map[variable]['units'],
                      'variable {} should have units {}'.format(variable, bounds_map[variable]['units'])
                  )
              else:
                  recommended_ctx.assert_true(
                      units != '',
                      'variable {} should have a units attribute that is not empty'.format(variable)
                  )
  
              comment = getattr(ncvar, 'comment', '')
              recommended_ctx.assert_true(
                  comment != '',
                  'variable {} should have a comment and not be empty'
              )
  
          return recommended_ctx.to_result()