def test_not_invisible(self):
        self.assertFalse(self.page.is_invisible('foobar'))
Convert a tree into spans (X, i, j) and add to a set.
dataset/ETHPy150Open edx/bok-choy/tests/test_visible.py/VisibleTest.test_not_invisible--crossover with--dataset/ETHPy150Open emilmont/pyStatParser/stat_parser/eval_parser.py/TreeOperations._convert_to_spans