bpo-36829: Add test.support.catch_unraisable_exception() (GH-13490)

* Copy test_exceptions.test_unraisable() to
  test_sys.UnraisableHookTest().
* Use catch_unraisable_exception() in test_coroutines,
  test_exceptions, test_generators.

Lib/test/test_sys.py

@@ -909,6 +909,47 @@ class UnraisableHookTest(unittest.TestCase):
         self.assertIn('Traceback (most recent call last):\n', err)
         self.assertIn('ValueError: 42\n', err)
 
+    def test_original_unraisablehook_err(self):
+        # bpo-22836: PyErr_WriteUnraisable() should give sensible reports
+        class BrokenDel:
+            def __del__(self):
+                exc = ValueError("del is broken")
+                # The following line is included in the traceback report:
+                raise exc
+
+        class BrokenStrException(Exception):
+            def __str__(self):
+                raise Exception("str() is broken")
+
+        class BrokenExceptionDel:
+            def __del__(self):
+                exc = BrokenStrException()
+                # The following line is included in the traceback report:
+                raise exc
+
+        for test_class in (BrokenDel, BrokenExceptionDel):
+            with self.subTest(test_class):
+                obj = test_class()
+                with test.support.captured_stderr() as stderr, \
+                     test.support.swap_attr(sys, 'unraisablehook',
+                                            sys.__unraisablehook__):
+                    # Trigger obj.__del__()
+                    del obj
+
+                report = stderr.getvalue()
+                self.assertIn("Exception ignored", report)
+                self.assertIn(test_class.__del__.__qualname__, report)
+                self.assertIn("test_sys.py", report)
+                self.assertIn("raise exc", report)
+                if test_class is BrokenExceptionDel:
+                    self.assertIn("BrokenStrException", report)
+                    self.assertIn("<exception str() failed>", report)
+                else:
+                    self.assertIn("ValueError", report)
+                    self.assertIn("del is broken", report)
+                self.assertTrue(report.endswith("\n"))
+
+
     def test_original_unraisablehook_wrong_type(self):
         exc = ValueError(42)
         with test.support.swap_attr(sys, 'unraisablehook',