Small fix for 3.14 setup

changedetectionio/tests/conftest.py

@@ -2,6 +2,7 @@
 import psutil
 import time
 from threading import Thread
+import multiprocessing
 
 import pytest
 import arrow
@@ -191,6 +192,34 @@ def cleanup(datastore_path):
             if os.path.isfile(f):
                 os.unlink(f)
 
+def pytest_configure(config):
+    """Configure pytest environment before tests run.
+
+    CRITICAL: Set multiprocessing start method to 'fork' for Python 3.14+ compatibility.
+
+    Python 3.14 changed the default start method from 'fork' to 'forkserver' on Linux.
+    The forkserver method requires all objects to be picklable, but pytest-flask's
+    LiveServer uses nested functions that can't be pickled.
+
+    Setting 'fork' explicitly:
+    - Maintains compatibility with Python 3.10-3.13 (where 'fork' was already default)
+    - Fixes Python 3.14 pickling errors
+    - Only affects Unix-like systems (Windows uses 'spawn' regardless)
+
+    See: https://github.com/python/cpython/issues/126831
+    See: https://docs.python.org/3/whatsnew/3.14.html
+    """
+    # Only set if not already set (respects existing configuration)
+    if multiprocessing.get_start_method(allow_none=True) is None:
+        try:
+            # 'fork' is available on Unix-like systems (Linux, macOS)
+            # On Windows, this will have no effect as 'spawn' is the only option
+            multiprocessing.set_start_method('fork', force=False)
+            logger.debug("Set multiprocessing start method to 'fork' for Python 3.14+ compatibility")
+        except (ValueError, RuntimeError):
+            # Already set, not available on this platform, or context already created
+            pass
+
 def pytest_addoption(parser):
     """Add custom command-line options for pytest.