Merge URLs properly on TestClient (#2376)

starlette/testclient.py

@@ -463,7 +463,7 @@ def request(  # type: ignore[override]
         ] = httpx._client.USE_CLIENT_DEFAULT,
         extensions: typing.Optional[typing.Dict[str, typing.Any]] = None,
     ) -> httpx.Response:
-        url = self.base_url.join(url)
+        url = self._merge_url(url)
         redirect = self._choose_redirect_arg(follow_redirects, allow_redirects)
         return super().request(
             method,

tests/middleware/test_session.py

@@ -130,7 +130,7 @@ def test_session_cookie_subpath(test_client_factory):
     )
     app = Starlette(routes=[Mount("/second_app", app=second_app)])
     client = test_client_factory(app, base_url="http://testserver/second_app")
-    response = client.post("/second_app/update_session", json={"some": "data"})
+    response = client.post("/update_session", json={"some": "data"})
     assert response.status_code == 200
     cookie = response.headers["set-cookie"]
     cookie_path_match = re.search(r"; path=(\S+);", cookie)

tests/test_testclient.py

@@ -354,3 +354,13 @@ def homepage(request: Request) -> JSONResponse:
     client = test_client_factory(app)
     response = client.get("/", headers=[("x-token", "foo"), ("x-token", "bar")])
     assert response.json() == {"x-token": ["foo", "bar"]}
+
+
+def test_merge_url(test_client_factory: Callable[..., TestClient]):
+    def homepage(request: Request) -> Response:
+        return Response(request.url.path)
+
+    app = Starlette(routes=[Route("/api/v1/bar", endpoint=homepage)])
+    client = test_client_factory(app, base_url="http://testserver/api/v1/")
+    response = client.get("/bar")
+    assert response.text == "/api/v1/bar"