fix test

tests/test_router_mount.py

@@ -1,19 +1,25 @@
-from fastapi import APIRouter, FastAPI
+from fastapi import FastAPI, APIRouter
+from fastapi.testclient import TestClient
 
-app = FastAPI()
-api_router = APIRouter(prefix="/api")
+
+def test_mount_on_router():
+    app = FastAPI()
+    api_router = APIRouter(prefix="/api")
 
     @api_router.get("/app")
     def read_main():
         return {"message": "Hello World from main app"}
 
-subapi = FastAPI()
+    subapi = FastAPI()
 
     @subapi.get("/sub")
     def read_sub():
         return {"message": "Hello World from sub API"}
 
-api_router.mount("/subapi", subapi)  # ← moved up
-app.include_router(api_router)       # ← now after
+    api_router.mount("/subapi", subapi)
+    app.include_router(api_router)
+
+    client = TestClient(app)
 
-print("All tests passed.")
+    assert client.get("/api/app").status_code == 200
+    assert client.get("/api/subapi/sub").status_code == 200