bpo-39386: Prevent double awaiting of async iterator (GH-18081)

Lib/test/test_asyncgen.py

@@ -1128,6 +1128,42 @@ class AsyncGenAsyncioTest(unittest.TestCase):
 
         self.assertEqual([], messages)
 
+    def test_async_gen_await_anext_twice(self):
+        async def async_iterate():
+            yield 1
+            yield 2
+
+        async def run():
+            it = async_iterate()
+            nxt = it.__anext__()
+            await nxt
+            with self.assertRaisesRegex(
+                    RuntimeError,
+                    r"cannot reuse already awaited __anext__\(\)/asend\(\)"
+            ):
+                await nxt
+
+            await it.aclose()  # prevent unfinished iterator warning
+
+        self.loop.run_until_complete(run())
+
+    def test_async_gen_await_aclose_twice(self):
+        async def async_iterate():
+            yield 1
+            yield 2
+
+        async def run():
+            it = async_iterate()
+            nxt = it.aclose()
+            await nxt
+            with self.assertRaisesRegex(
+                    RuntimeError,
+                    r"cannot reuse already awaited aclose\(\)/athrow\(\)"
+            ):
+                await nxt
+
+        self.loop.run_until_complete(run())
+
 
 if __name__ == "__main__":
     unittest.main()