[3.12] gh-105071: add PyUnstable_Exc_PrepReraiseStar to expose except* implementation in the unstable API (GH-105072) (#105095)

(cherry picked from commit b7aadb4583)

Lib/test/test_capi/test_exceptions.py

@@ -5,6 +5,7 @@ import unittest
 from test import support
 from test.support import import_helper
 from test.support.script_helper import assert_python_failure
+from test.support.testcase import ExceptionIsLikeMixin
 
 from .test_misc import decode_stderr
 
@@ -189,5 +190,97 @@ class Test_ErrSetAndRestore(unittest.TestCase):
                          'Normalization failed: type=Broken args=<unknown>')
 
 
+class Test_PyUnstable_Exc_PrepReraiseStar(ExceptionIsLikeMixin, unittest.TestCase):
+
+    def setUp(self):
+        super().setUp()
+        try:
+            raise ExceptionGroup("eg", [TypeError('bad type'), ValueError(42)])
+        except ExceptionGroup as e:
+            self.orig = e
+
+    def test_invalid_args(self):
+        with self.assertRaisesRegex(TypeError, "orig must be an exception"):
+            _testcapi.unstable_exc_prep_reraise_star(42, [None])
+
+        with self.assertRaisesRegex(TypeError, "excs must be a list"):
+            _testcapi.unstable_exc_prep_reraise_star(self.orig, 42)
+
+        with self.assertRaisesRegex(TypeError, "not an exception"):
+            _testcapi.unstable_exc_prep_reraise_star(self.orig, [TypeError(42), 42])
+
+        with self.assertRaisesRegex(ValueError, "orig must be a raised exception"):
+            _testcapi.unstable_exc_prep_reraise_star(ValueError(42), [TypeError(42)])
+
+        with self.assertRaisesRegex(ValueError, "orig must be a raised exception"):
+            _testcapi.unstable_exc_prep_reraise_star(ExceptionGroup("eg", [ValueError(42)]),
+                                                     [TypeError(42)])
+
+
+    def test_nothing_to_reraise(self):
+        self.assertEqual(
+            _testcapi.unstable_exc_prep_reraise_star(self.orig, [None]), None)
+
+        try:
+            raise ValueError(42)
+        except ValueError as e:
+            orig = e
+        self.assertEqual(
+            _testcapi.unstable_exc_prep_reraise_star(orig, [None]), None)
+
+    def test_reraise_orig(self):
+        orig = self.orig
+        res = _testcapi.unstable_exc_prep_reraise_star(orig, [orig])
+        self.assertExceptionIsLike(res, orig)
+
+    def test_raise_orig_parts(self):
+        orig = self.orig
+        match, rest = orig.split(TypeError)
+
+        test_cases = [
+            ([match, rest], orig),
+            ([rest, match], orig),
+            ([match], match),
+            ([rest], rest),
+            ([], None),
+        ]
+
+        for input, expected in test_cases:
+            with self.subTest(input=input):
+                res = _testcapi.unstable_exc_prep_reraise_star(orig, input)
+                self.assertExceptionIsLike(res, expected)
+
+
+    def test_raise_with_new_exceptions(self):
+        orig = self.orig
+
+        match, rest = orig.split(TypeError)
+        new1 = OSError('bad file')
+        new2 = RuntimeError('bad runtime')
+
+        test_cases = [
+            ([new1, match, rest], ExceptionGroup("", [new1, orig])),
+            ([match, new1, rest], ExceptionGroup("", [new1, orig])),
+            ([match, rest, new1], ExceptionGroup("", [new1, orig])),
+
+            ([new1, new2, match, rest], ExceptionGroup("", [new1, new2, orig])),
+            ([new1, match, new2, rest], ExceptionGroup("", [new1, new2, orig])),
+            ([new2, rest, match, new1], ExceptionGroup("", [new2, new1, orig])),
+            ([rest, new2, match, new1], ExceptionGroup("", [new2, new1, orig])),
+
+
+            ([new1, new2, rest], ExceptionGroup("", [new1, new2, rest])),
+            ([new1, match, new2], ExceptionGroup("", [new1, new2, match])),
+            ([rest, new2, new1], ExceptionGroup("", [new2, new1, rest])),
+            ([new1, new2], ExceptionGroup("", [new1, new2])),
+            ([new2, new1], ExceptionGroup("", [new2, new1])),
+        ]
+
+        for (input, expected) in test_cases:
+            with self.subTest(input=input):
+                res = _testcapi.unstable_exc_prep_reraise_star(orig, input)
+                self.assertExceptionIsLike(res, expected)
+
+
 if __name__ == "__main__":
     unittest.main()