test: Update tests/test_exceptions.py to include coverage for in [m…

…iddleware/exceptions.py](https://github.com/encode/starlette/blob/master/starlette/middleware/exceptions.py#L31) (encode#2452)

tests/test_exceptions.py

@@ -33,20 +33,6 @@ def with_headers(request: Request) -> None:
     raise HTTPException(status_code=200, headers={"x-potato": "always"})
 
 
-class BadBodyException(HTTPException):
-    pass
-
-
-async def read_body_and_raise_exc(request: Request) -> None:
-    await request.body()
-    raise BadBodyException(422)
-
-
-async def handler_that_reads_body(request: Request, exc: BadBodyException) -> JSONResponse:
-    body = await request.body()
-    return JSONResponse(status_code=422, content={"body": body.decode()})
-
-
 class HandledExcAfterResponse:
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         response = PlainTextResponse("OK", status_code=200)
@@ -63,15 +49,11 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         Route("/with_headers", endpoint=with_headers),
         Route("/handled_exc_after_response", endpoint=HandledExcAfterResponse()),
         WebSocketRoute("/runtime_error", endpoint=raise_runtime_error),
-        Route("/consume_body_in_endpoint_and_handler", endpoint=read_body_and_raise_exc, methods=["POST"]),
     ]
 )
 
 
-app = ExceptionMiddleware(
-    router,
-    handlers={BadBodyException: handler_that_reads_body},  # type: ignore[dict-item]
-)
+app = ExceptionMiddleware(router, handlers=None)
 
 
 @pytest.fixture
@@ -194,7 +176,31 @@ def test_exception_middleware_deprecation() -> None:
         starlette.exceptions.ExceptionMiddleware
 
 
-def test_request_in_app_and_handler_is_the_same_object(client: TestClient) -> None:
-    response = client.post("/consume_body_in_endpoint_and_handler", content=b"Hello!")
+class BadBodyException(HTTPException):
+    pass
+
+
+async def read_body_and_raise_exc(request: Request) -> None:
+    await request.body()
+    raise BadBodyException(422)
+
+
+async def handler_that_reads_body(request: Request, exc: BadBodyException) -> JSONResponse:
+    body = await request.body()
+    return JSONResponse(status_code=422, content={"body": body.decode()})
+
+
+def test_request_in_app_and_handler_is_the_same_object(test_client_factory: TestClientFactory) -> None:
+    app = ExceptionMiddleware(
+        Router(
+            routes=[
+                Route("/consume_body_in_endpoint_and_handler", endpoint=read_body_and_raise_exc, methods=["POST"]),
+            ]
+        ),
+        handlers={BadBodyException: handler_that_reads_body},  # type: ignore[dict-item]
+    )
+    with test_client_factory(app) as client:
+        response = client.post("/consume_body_in_endpoint_and_handler", content=b"Hello!")
+
     assert response.status_code == 422
     assert response.json() == {"body": "Hello!"}