[v1.x] Expire idle Streamable HTTP sessions by default and cap concurrent sessions (#3426)

tests/conftest.py

@@ -1,6 +1,27 @@
+from collections.abc import Iterator
+
 import pytest
+from sse_starlette.sse import AppStatus
 
 
 @pytest.fixture
 def anyio_backend():
     return "asyncio"
+
+
+@pytest.fixture(autouse=True)
+def reset_sse_starlette_exit_event() -> Iterator[None]:
+    """sse-starlette<2 caches a module-level anyio.Event on AppStatus. Clear it
+    around each test so it is never bound to a closed event loop: any test that
+    serves an SSE response in process would otherwise inherit the event a
+    previous test created on another loop. Clearing it afterwards matters too,
+    because later test modules fork uvicorn subprocesses on Linux and would
+    otherwise inherit a stale event."""
+
+    def clear() -> None:
+        if hasattr(AppStatus, "should_exit_event"):  # pragma: no cover
+            setattr(AppStatus, "should_exit_event", None)
+
+    clear()
+    yield
+    clear()