Ensure IPython's HistoryManager threads don't leak

Author: davidbrochart

tests/conftest.py

@@ -11,6 +11,7 @@
 import zmq.asyncio
 from anyio import create_memory_object_stream, create_task_group
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
+from IPython.core.history import HistoryManager
 from jupyter_client.session import Session
 
 from ipykernel.ipkernel import IPythonKernel
@@ -29,6 +30,10 @@
     tracemalloc = None
 
 
+# ensure we don't leak history managers
+HistoryManager._max_inst = 1
+
+
 @pytest.fixture()
 def anyio_backend():
     return "asyncio"