Don't group duplicated headers on a single string on the TestClient

starlette/testclient.py

@@ -223,10 +223,7 @@ def handle_request(self, request: httpx.Request) -> httpx.Response:
             headers = [(b"host", (f"{host}:{port}").encode())]
 
         # Include other request headers.
-        headers += [
-            (key.lower().encode(), value.encode())
-            for key, value in request.headers.items()
-        ]
+        headers += [(key, value) for _, key, value in request.headers._list]
 
         scope: typing.Dict[str, typing.Any]
 

tests/test_testclient.py

@@ -2,6 +2,7 @@
 import sys
 from asyncio import current_task as asyncio_current_task
 from contextlib import asynccontextmanager
+from typing import Callable, Dict, List, Tuple
 
 import anyio
 import pytest
@@ -10,6 +11,7 @@
 
 from starlette.applications import Starlette
 from starlette.middleware import Middleware
+from starlette.requests import Request
 from starlette.responses import JSONResponse, RedirectResponse, Response
 from starlette.routing import Route
 from starlette.testclient import TestClient
@@ -342,3 +344,21 @@ async def app(scope, receive, send):
     client = test_client_factory(app, follow_redirects=False)
     response = client.get("/")
     assert response.status_code == 307
+
+
+@pytest.mark.parametrize(
+    "headers,expected_response",
+    [([("x-token", "foo"), ("x-token", "bar")], {"x-token": ["foo", "bar"]})],
+)
+def test_headers_with_duplicate_field_name(
+    headers: List[Tuple[str, str]],
+    expected_response: Dict[str, List[str]],
+    test_client_factory: Callable[[Starlette], TestClient],
+):
+    def homepage(request: Request) -> JSONResponse:
+        return JSONResponse({"x-token": request.headers.getlist("x-token")})
+
+    app = Starlette(routes=[Route("/", endpoint=homepage)])
+    client = test_client_factory(app)
+    response = client.get("/", headers=headers)
+    assert response.json() == expected_response