add tests for duplicate special dependency bug fix

tests/test_duplicate_special_dependencies.py

@@ -0,0 +1,62 @@
+import pytest
+from fastapi import BackgroundTasks, FastAPI, Request, Response, WebSocket
+from fastapi.security import SecurityScopes
+from fastapi.testclient import TestClient
+
+app = FastAPI()
+
+
+@app.get("/request")
+def request(r1: Request, r2: Request) -> str:
+    assert r1 is not None
+    assert r1 is r2
+    return "success"
+
+
+@app.get("/response")
+def response(r1: Response, r2: Response) -> str:
+    assert r1 is not None
+    assert r1 is r2
+    return "success"
+
+
+@app.get("/background-tasks")
+def background_tasks(t1: BackgroundTasks, t2: BackgroundTasks) -> str:
+    assert t1 is not None
+    assert t1 is t2
+    return "success"
+
+
+@app.get("/websocket")
+def websocket(ws1: WebSocket, ws2: WebSocket) -> str:
+    assert ws1 is not None
+    assert ws1 is ws2
+    return "success"
+
+
+@app.get("/security-scopes")
+def security_scopes(sc1: SecurityScopes, sc2: SecurityScopes) -> str:
+    assert sc1 is not None
+    assert sc1 is sc2
+    return "success"
+
+
+client = TestClient(app)
+
+
+@pytest.mark.parametrize(
+    "url",
+    (
+        "/request",
+        "/response",
+        "/background-tasks",
+        "/security-scopes",
+    ),
+)
+def test_duplicate_special_dependency(url: str) -> None:
+    assert client.get(url).text == '"success"'
+
+
+def test_duplicate_websocket_dependency() -> None:
+    # Raises exception if connect fails.
+    client.websocket_connect("/websocket")