fix regex split for subtest names

[eleanorjboyd]

fixes #21733.

Handles both cases of subtest naming as described here by ChatGPT:

When you use self.subTest(i=i), you're explicitly naming the argument i. This causes subTest to use the key=value format for the sub-test's description. Therefore, the sub-test name becomes:

test_subtests.NumbersTest2.test_even2 (i='h i')

However, when you use self.subTest(i), you're passing a positional argument. In this case, subTest doesn't have a key for the argument, so it simply uses the value in square brackets:

test_subtests.NumbersTest2.test_even2 [h i]

[alisonatwork]

Hi @eleanorjboyd and @rzhao271 / @roblourens. I already commented on #21733, but I didn't realize you were parsing the unittest output directly and therefore have to deal with whatever extra brackets it is inserting. In that case, this test is correct but also misleading, because you can't do with self.subTest(value1, value2) - that will result in a Python TypeError, on 3.10 at least.

As per the subTest documentation (https://docs.python.org/3/library/unittest.html#unittest.TestCase.subTest), the only choices are to pass a string (msg) or to pass kwargs (**params) or to pass both. I just tested now and if you pass both a string and a kwargs, then it will print both the string in square brackets and the kwargs in round brackets, so your current regex may not handle that case.

It might be useful to have an end-to-end test for this stuff, i.e. first create some real-world Python unit tests that are run with the targeted versions of Python, then use the output of those as the input for the VS Code parser. This way you can be sure that if the Python default test runner changes its output format in a future version, it won't mysteriously break the VS Code parsing which was expecting something different. Alternatively - and I am not sure how hard this would be to do - VS Code could have its own test runner, which should allow access to the internal data structures that Python unittest is using, and then you could create a nice JSON structure to enable all kinds of cool front end features (e.g. filter by individual kwarg).