docs(CHANGES) Note move of test helpers

Author: tony

CHANGES

@@ -15,6 +15,41 @@ $ pip install --user --upgrade --pre libtmux
 
 - _Future release notes will be placed here_
 
+### Breaking Changes
+
+#### Test helpers: Refactor
+
+Test helper functionality has been split into focused modules (#XXX):
+
+- `libtmux.test` module split into:
+  - `libtmux.test.constants`: Test-related constants (`TEST_SESSION_PREFIX`, etc.)
+  - `libtmux.test.environment`: Environment variable mocking
+  - `libtmux.test.random`: Random string generation utilities
+  - `libtmux.test.temporary`: Temporary session/window management
+
+**Breaking**: Import paths have changed. Update imports:
+
+```python
+# Old (0.45.x and earlier)
+from libtmux.test import (
+    TEST_SESSION_PREFIX,
+    get_test_session_name,
+    get_test_window_name,
+    namer,
+    temp_session,
+    temp_window,
+    EnvironmentVarGuard,
+)
+```
+
+```python
+# New (0.46.0+)
+from libtmux.test.constants import TEST_SESSION_PREFIX
+from libtmux.test.environment import EnvironmentVarGuard
+from libtmux.test.random import get_test_session_name, get_test_window_name, namer
+from libtmux.test.temporary import temp_session, temp_window
+```
+
 ### Development
 
 - CI: Check for runtime dependencies (#574)