allow exceptions in middleware to surface when using TestClient (#888)

starlette/testclient.py

@@ -471,6 +471,8 @@ class TestClient(requests.Session):
     async def wait_startup(self) -> None:
         await self.receive_queue.put({"type": "lifespan.startup"})
         message = await self.send_queue.get()
+        if message is None:
+            self.task.result()
         assert message["type"] in (
             "lifespan.startup.complete",
             "lifespan.startup.failed",

tests/test_testclient.py

@@ -3,6 +3,7 @@ import asyncio
 import pytest
 
 from starlette.applications import Starlette
+from starlette.middleware import Middleware
 from starlette.responses import JSONResponse
 from starlette.testclient import TestClient
 from starlette.websockets import WebSocket, WebSocketDisconnect
@@ -56,6 +57,25 @@ def test_error_on_startup():
             pass  # pragma: no cover
 
 
+def test_exception_in_middleware():
+
+    class MiddlewareException(Exception):
+        pass
+
+    class BrokenMiddleware:
+        def __init__(self, app):
+            self.app = app
+
+        async def __call__(self, scope, receive, send):
+            raise MiddlewareException()
+
+    broken_middleware = Starlette(middleware=[Middleware(BrokenMiddleware)])
+
+    with pytest.raises(MiddlewareException):
+        with TestClient(broken_middleware):
+            pass  # pragma: no cover
+
+
 def test_testclient_asgi2():
     def app(scope):
         async def inner(receive, send):