bpo-39101: Fixes BaseException hang in IsolatedAsyncioTestCase. (GH-22654)

(cherry picked from commit 8374d2ee15)

Co-authored-by: Lisa Roach <lisaroach14@gmail.com>

Lib/unittest/test/test_async_case.py

@@ -190,6 +190,33 @@ async def on_async_cleanup(self, val):
                                   'async_cleanup 2',
                                   'sync_cleanup 1'])
 
+    def test_base_exception_from_async_method(self):
+        events = []
+        class Test(unittest.IsolatedAsyncioTestCase):
+            async def test_base(self):
+                events.append("test_base")
+                raise BaseException()
+                events.append("not it")
+
+            async def test_no_err(self):
+                events.append("test_no_err")
+
+            async def test_cancel(self):
+                raise asyncio.CancelledError()
+
+        test = Test("test_base")
+        output = test.run()
+        self.assertFalse(output.wasSuccessful())
+
+        test = Test("test_no_err")
+        test.run()
+        self.assertEqual(events, ['test_base', 'test_no_err'])
+
+        test = Test("test_cancel")
+        output = test.run()
+        self.assertFalse(output.wasSuccessful())
+
+
 
 if __name__ == "__main__":
     unittest.main()