code: def test_subscribe() -> None:
      d = Document()
      s = bss.ServerSession("some-id", d, "ioloop")
      assert s.connection_count == 0
      s.subscribe("connection1")
      assert s.connection_count == 1
      s.subscribe("connection2")
      assert s.connection_count == 2
      s.unsubscribe("connection1")
      assert s.connection_count == 1
      s.unsubscribe("connection2")
      assert s.connection_count == 0
  
file_path: bokeh/tests/unit/bokeh/server/test_session__server.py
imports: from __future__ import annotations
  import pytest
  from unittest import mock
  from bokeh.document import Document
  import bokeh.server.session
label_desc: Use image node_id 2 for calling a global function with example usage: test_subscribe() without return types