How to use the executing.NotOneValueFound function in executing

def test_comprehensions(self):
        # Comprehensions can be separated if they contain different names
        str([{tester(x) for x in [1]}, {tester(y) for y in [1]}])
        # or are on different lines
        str([{tester(x) for x in [1]},
             {tester(x) for x in [1]}])
        # or are of different types
        str([{tester(x) for x in [1]}, list(tester(x) for x in [1])])
        # but not if everything is the same
        # noinspection PyTypeChecker
        with self.assertRaises(NotOneValueFound):
            str([{tester(x) for x in [1]}, {tester(x) for x in [2]}])

def test_only(self):
        for n in range(5):
            gen = (i for i in range(n))
            if n == 1:
                self.assertEqual(only(gen), 0)
            else:
                with self.assertRaises(NotOneValueFound):
                    only(gen)

def test_only(self):
        for n in range(5):
            gen = (i for i in range(n))
            if n == 1:
                self.assertEqual(only(gen), 0)
            else:
                with self.assertRaises(NotOneValueFound):
                    only(gen)