def METHOD_NAME(self, mock_render_html):
    mock_render_html.return_value = 'Column'
    col1 = DataTablesColumn(name='test-column1')
    col2 = DataTablesColumn(name='test-column2')
    group = DataTablesColumnGroup('test-group')
    group.add_column(col1)
    group.add_column(col2)
    self.assertEqual(group.render_group_html, 'Column\nColumn')