From 38786d190566d721714491d01d810a4930dd2028 Mon Sep 17 00:00:00 2001
From: Niler Barcelos <nilerbarcelos@gmail.com>
Date: Tue, 17 Mar 2026 14:20:48 -0300
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Fix=20AssertionError=20when=20us?=
 =?UTF-8?q?ing=20TestClient=20directly=20with=20APIRouter=20(#14128)?=
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---
 fastapi/routing.py                     |  5 +++
 tests/test_router_direct_testclient.py | 62 ++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 tests/test_router_direct_testclient.py

diff --git a/fastapi/routing.py b/fastapi/routing.py
index 36acb6b89d..173a6a5a0a 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -115,6 +115,11 @@ def request_response(
             response_awaited = False
             async with AsyncExitStack() as request_stack:
                 scope["fastapi_inner_astack"] = request_stack
+                # Ensure fastapi_middleware_astack exists in scope even when
+                # the router is used directly without a FastAPI app (which
+                # normally sets it up via AsyncExitStackMiddleware).
+                if "fastapi_middleware_astack" not in scope:
+                    scope["fastapi_middleware_astack"] = request_stack
                 async with AsyncExitStack() as function_stack:
                     scope["fastapi_function_astack"] = function_stack
                     response = await f(request)
diff --git a/tests/test_router_direct_testclient.py b/tests/test_router_direct_testclient.py
new file mode 100644
index 0000000000..569f334992
--- /dev/null
+++ b/tests/test_router_direct_testclient.py
@@ -0,0 +1,62 @@
+"""Test for issue #14128: Router used directly with TestClient and yield dependencies."""
+
+from fastapi import APIRouter, Depends
+from fastapi.testclient import TestClient
+
+
+def test_router_direct_testclient_with_yield_dependency():
+    """TestClient(router) should work even without wrapping in FastAPI()."""
+    router = APIRouter()
+
+    async def yield_dep():
+        yield "value"
+
+    @router.get("/test")
+    async def endpoint(dep: str = Depends(yield_dep)):
+        return {"dep": dep}
+
+    client = TestClient(router)
+    response = client.get("/test")
+    assert response.status_code == 200
+    assert response.json() == {"dep": "value"}
+
+
+def test_router_direct_testclient_with_multiple_yield_dependencies():
+    """Multiple yield dependencies should work with direct router TestClient."""
+    router = APIRouter()
+
+    async def dep_a():
+        yield "a"
+
+    async def dep_b():
+        yield "b"
+
+    @router.get("/test")
+    async def endpoint(a: str = Depends(dep_a), b: str = Depends(dep_b)):
+        return {"a": a, "b": b}
+
+    client = TestClient(router)
+    response = client.get("/test")
+    assert response.status_code == 200
+    assert response.json() == {"a": "a", "b": "b"}
+
+
+def test_router_direct_testclient_yield_dependency_cleanup():
+    """Yield dependency cleanup should run even with direct router TestClient."""
+    cleaned_up = False
+
+    router = APIRouter()
+
+    async def yield_dep():
+        nonlocal cleaned_up
+        yield "value"
+        cleaned_up = True
+
+    @router.get("/test")
+    async def endpoint(dep: str = Depends(yield_dep)):
+        return {"dep": dep}
+
+    client = TestClient(router)
+    response = client.get("/test")
+    assert response.status_code == 200
+    assert cleaned_up