diff --git a/tests/test_router_mount.py b/tests/test_router_mount.py
index 0a36544c9..9bee074f4 100644
--- a/tests/test_router_mount.py
+++ b/tests/test_router_mount.py
@@ -1,20 +1,25 @@
 from fastapi import FastAPI, APIRouter
 from fastapi.testclient import TestClient
 
-app = FastAPI()
-api_router = APIRouter(prefix="/api")
 
-@api_router.get("/app")
-def read_main():
-    return {"message": "Hello World from main app"}
+def test_mount_on_router():
+    app = FastAPI()
+    api_router = APIRouter(prefix="/api")
 
-subapi = FastAPI()
+    @api_router.get("/app")
+    def read_main():
+        return {"message": "Hello World from main app"}
 
-@subapi.get("/sub")
-def read_sub():
-    return {"message": "Hello World from sub API"}
+    subapi = FastAPI()
 
-api_router.mount("/subapi", subapi)  # ← moved up
-app.include_router(api_router)       # ← now after
+    @subapi.get("/sub")
+    def read_sub():
+        return {"message": "Hello World from sub API"}
 
-print("All tests passed.")
\ No newline at end of file
+    api_router.mount("/subapi", subapi)
+    app.include_router(api_router)
+
+    client = TestClient(app)
+
+    assert client.get("/api/app").status_code == 200
+    assert client.get("/api/subapi/sub").status_code == 200
\ No newline at end of file