chore: import upstream snapshot with attribution

tests/utils/test_simple_session.py

@@ -0,0 +1,54 @@
+from __future__ import annotations
+
+from typing import cast
+
+import pytest
+
+from agents.items import TResponseInputItem
+from tests.utils.simple_session import CountingSession, IdStrippingSession, SimpleListSession
+
+
+@pytest.mark.asyncio
+async def test_simple_list_session_preserves_history_and_saved_items() -> None:
+    history: list[TResponseInputItem] = [
+        cast(TResponseInputItem, {"id": "msg1", "content": "hi", "role": "user"}),
+        cast(TResponseInputItem, {"id": "msg2", "content": "hello", "role": "assistant"}),
+    ]
+    session = SimpleListSession(history=history)
+
+    items = await session.get_items()
+    # get_items should return a copy, not the original list.
+    assert items == history
+    assert items is not history
+    # saved_items should mirror the stored list.
+    assert session.saved_items == history
+
+
+@pytest.mark.asyncio
+async def test_counting_session_tracks_pop_calls() -> None:
+    session = CountingSession(
+        history=[cast(TResponseInputItem, {"id": "x", "content": "hi", "role": "user"})]
+    )
+
+    assert session.pop_calls == 0
+    await session.pop_item()
+    assert session.pop_calls == 1
+    await session.pop_item()
+    assert session.pop_calls == 2
+
+
+@pytest.mark.asyncio
+async def test_id_stripping_session_removes_ids_on_add() -> None:
+    session = IdStrippingSession()
+    items: list[TResponseInputItem] = [
+        cast(TResponseInputItem, {"id": "keep-removed", "content": "hello", "role": "user"}),
+        cast(TResponseInputItem, {"content": "no-id", "role": "assistant"}),
+    ]
+
+    await session.add_items(items)
+    stored = await session.get_items()
+
+    assert all("id" not in item for item in stored if isinstance(item, dict))
+    # pop_calls should increment when rewinding.
+    await session.pop_item()
+    assert session.pop_calls == 1