            self.frame.group_by('colors', {'colors': self.context.agg.sum})

    def test_stats_on_string_var(self):
        """Non-numeric aggregates error on non-numeric column"""
        with self.assertRaises(Exception):
            self.frame.group_by('colors', {'colors': self.context.agg.var})

    def test_invalid_column_name(self):
        """Aggregate on non-existant column errors"""
        with self.assertRaises(Exception):
            self.frame.group_by(
                'InvalidColumnName', {'colors': self.context.agg.var})