test: ensure mp_start runs on startup

tests/conftest.py

@@ -21,6 +21,7 @@ from freqtrade.exchange import Exchange, timeframe_to_minutes, timeframe_to_seco
 from freqtrade.freqtradebot import FreqtradeBot
 from freqtrade.persistence import LocalTrade, Order, Trade, init_db
 from freqtrade.resolvers import ExchangeResolver
+from freqtrade.system import set_mp_start_method
 from freqtrade.util import dt_now, dt_ts
 from freqtrade.worker import Worker
 from tests.conftest_trades import (
@@ -500,6 +501,15 @@ def patch_gc(mocker) -> None:
     mocker.patch("freqtrade.main.gc_set_threshold")
 
 
+@pytest.fixture(scope="session", autouse=True)
+def fixture_set_mp_start_method():
+    """
+    Patch multiprocessing start mode globally
+    Auto-used, runs once per session.
+    """
+    set_mp_start_method()
+
+
 def is_arm(include_aarch64: bool = False) -> bool:
     machine = platform.machine()
     if include_aarch64: