add tests for deferred route initialization

remove useless checks in test

test defer_init flag on route

add route to test app

fix coverage again

tests/test_route_deferred_init.py

@@ -0,0 +1,106 @@
+from typing import List, Optional
+
+from fastapi import APIRouter, Depends, FastAPI
+from fastapi.routing import APIRoute
+from fastapi.testclient import TestClient
+from pydantic import BaseModel
+from starlette.routing import BaseRoute
+
+deferred_keys = [
+    "app",
+    "response_fields",
+    "body_field",
+    "response_field",
+    "secure_cloned_response_field",
+    "dependant",
+    "_flat_dependant",
+    "_embed_body_fields",
+]
+
+
+def check_if_initialized(route: APIRoute, should_not: bool = False):
+    for key in deferred_keys:
+        if should_not:
+            assert key not in route.__dict__
+        else:
+            assert key in route.__dict__
+
+
+def create_test_router(
+    routes: Optional[List[BaseRoute]] = None, defer_init: bool = True
+):
+    router = APIRouter(routes=routes or [], defer_init=defer_init)
+
+    class UserIdBody(BaseModel):
+        user_id: int
+
+    @router.get("/user_id", dependencies=[Depends(lambda: True)])
+    async def get_user_id(user_id: int = Depends(lambda: 1)) -> UserIdBody:
+        return {"user_id": user_id}
+
+    return router
+
+
+def test_route_defers():
+    app = FastAPI()
+    router = create_test_router(routes=app.router.routes)
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route, should_not=True)
+
+    app.router = router
+    client = TestClient(app)
+    response = client.get("/user_id")
+    assert response.status_code == 200
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+
+def test_route_manual_init():
+    router = create_test_router()
+    for route in router.routes:
+        check_if_initialized(route, should_not=True)
+        route.init_attributes()
+        check_if_initialized(route)
+
+    router = create_test_router()
+    router.init_routes()
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_router_defer_init_flag():
+    route = APIRoute("/test", lambda: {"test": True}, defer_init=False)
+    check_if_initialized(route)
+
+    deferring_router = create_test_router()
+    router = create_test_router(routes=deferring_router.routes, defer_init=False)
+
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_root_router_always_initialized():
+    app = FastAPI()
+
+    @app.get("/test")
+    async def test_get():
+        return {"test": 1}
+
+    router = create_test_router()
+    app.include_router(router)
+    for route in app.router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+    client = TestClient(app)
+    response = client.get("/test")
+    assert response.status_code == 200