[agronholm]

Adds tests for except* handlers that raise a BaseException that isn't an Exception. Until now, every handler in test_except_star.py raised an Exception subclass. This changes tests only; CPython already behaves correctly.

Why

PyPy runs CPython's test_except_star.py and passes all of it, but gets this case wrong (pypy/pypy#5689). Its except* re-raise logic asserts that every exception raised in a handler is an Exception, so raising e.g. KeyboardInterrupt from a handler produces an internal AssertionError. Fixing that alone exposes a second bug: it builds an ExceptionGroup where CPython builds a BaseExceptionGroup, which fails with TypeError: Cannot nest BaseExceptions in an ExceptionGroup. Neither bug was noticed because no test covered this case. It only came up through a test in the exceptiongroup backport (agronholm/exceptiongroup#163), which now skips that test on PyPy.

New tests in TestExceptStarRaise

They follow the existing test_raise_* tests, but raise a local BaseException subclass. I used a local subclass rather than KeyboardInterrupt so that a broken implementation can't stop the test run by letting a KeyboardInterrupt escape.

• test_raise_base_exception: part of the group is handled, so the result must be a BaseExceptionGroup holding the raised exception and the unhandled rest.
• test_raise_handle_all_raise_one_base_exception: the whole group is handled, so the raised exception propagates on its own.
• test_raise_handle_all_raise_base_exception_and_exception: two handlers raise a BaseException and an Exception, so the result must be a BaseExceptionGroup.

The two group tests check the group's type and members directly. assertExceptionIsLike only looks inside ExceptionGroup instances; given a BaseExceptionGroup, it compares just the class and message.

Testing

• CPython main (debug build): ./python -m test test_except_star passes (63 tests), and -R 3:3 reports no leaks.
• I added the same tests to PyPy's copy of test_except_star.py:
  • PyPy 8.0.0 (3.12) release: all 3 new tests fail.
  • PyPy py3.12 from source with only the AssertionError fixed: the 2 tests expecting a BaseExceptionGroup fail.
  • PyPy py3.12 from source with both fixes from except*: AssertionError when a handler raises a non-Exception BaseException (e.g. KeyboardInterrupt) pypy/pypy#5689: all pass.

No NEWS entry, since this only adds tests.

• Issue: test_except_star does not cover except* handlers raising a non-Exception BaseException #160659