Checks that if a variable exists for the trajectory id it has the appropriate attributes

        :param netCDF4.Dataset dataset: An open netCDF dataset

def check_trajectory_id(self, dataset):
        '''
        Checks that if a variable exists for the trajectory id it has the appropriate attributes

        :param netCDF4.Dataset dataset: An open netCDF dataset
        '''
        results = []
        exists_ctx = TestCtx(BaseCheck.MEDIUM, 'Variable defining "trajectory_id" exists')
        trajectory_ids = dataset.get_variables_by_attributes(cf_role='trajectory_id')
        # No need to check
        exists_ctx.assert_true(trajectory_ids, 'variable defining cf_role="trajectory_id" exists')
        if not trajectory_ids:
            return exists_ctx.to_result()
        results.append(exists_ctx.to_result())
        test_ctx = TestCtx(BaseCheck.MEDIUM, 'Recommended attributes for the {} variable'.format(trajectory_ids[0].name))
        test_ctx.assert_true(
            getattr(trajectory_ids[0], 'long_name', '') != "",
            "long_name attribute should exist and not be empty"
        )
        results.append(test_ctx.to_result())
        return results