test: run_sync tests

nbclient/tests/util.py

@@ -0,0 +1,58 @@
+import asyncio
+
+import tornado
+
+from nbclient.util import run_sync
+
+
+@run_sync
+async def some_async_function():
+    await asyncio.sleep(0.01)
+    return 42
+
+
+def test_nested_asyncio_with_existing_ioloop():
+    ioloop = asyncio.new_event_loop()
+    try:
+        asyncio.set_event_loop(ioloop)
+        assert some_async_function() == 42
+        assert asyncio.get_event_loop() is ioloop
+        print(ioloop, id(ioloop))
+    finally:
+        asyncio._set_running_loop(None)  # it seems nest_asyncio doesn't reset this
+
+
+def test_nested_asyncio_with_no_ioloop():
+    asyncio.set_event_loop(None)
+    try:
+        assert some_async_function() == 42
+    finally:
+        asyncio._set_running_loop(None)  # it seems nest_asyncio doesn't reset this
+
+
+def test_nested_asyncio_with_tornado():
+    # This tests if tornado accepts the pure-Python Futures, see
+    # https://github.com/tornadoweb/tornado/issues/2753
+    # https://github.com/erdewit/nest_asyncio/issues/23
+    asyncio.set_event_loop(asyncio.new_event_loop())
+    ioloop = tornado.ioloop.IOLoop.current()
+
+    async def some_async_function():
+        future = asyncio.ensure_future(asyncio.sleep(0.1))
+        # this future is a different future after nested-asyncio has patched
+        # the asyncio module, check if tornado likes it:
+        ioloop.add_future(future, lambda f: f.result())
+        await future
+        return 42
+
+    def some_sync_function():
+        return run_sync(some_async_function)()
+
+    async def run():
+        # calling some_async_function directly should work
+        assert await some_async_function() == 42
+        # but via a sync function (using nested-asyncio) can lead to issues:
+        # https://github.com/tornadoweb/tornado/issues/2753
+        assert some_sync_function() == 42
+
+    ioloop.run_sync(run)