fix test

tests/test_router_mount.py

@@ -1,5 +1,8 @@
-from fastapi import APIRouter, FastAPI
+from fastapi import FastAPI, APIRouter
+from fastapi.testclient import TestClient
 
+
+def test_mount_on_router():
     app = FastAPI()
     api_router = APIRouter(prefix="/api")
 
@@ -13,7 +16,10 @@ subapi = FastAPI()
     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