fix(testing): return [] instead of None from get_logs for non-Chrome browsers

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#3826](https://github.com/plotly/dash/pull/3826) WebSocket callback dispatch no longer lets long-lived callbacks limit the number of concurrent users. Async callbacks (including session-persistent ones) run directly on the connection event loop instead of occupying a worker thread, and synchronous callbacks run on a shared `ThreadPoolExecutor` whose size is configurable via the new `websocket_max_workers` argument to `Dash` (default `4`). A synchronous persistent (no-output) callback now warns at registration since it would tie up a worker thread.
 
 ## Fixed
+- [#3779](https://github.com/plotly/dash/pull/3779) Fix `dash.testing` `Browser.get_logs()` returning `None` on non-Chrome webdrivers, which broke assertions like `assert dash_duo.get_logs() == []`. It now returns `[]`, matching the Chrome code path.
 - [#3822](https://github.com/plotly/dash/pull/3822) Fix `UnboundLocalError` for `user_callback_output` in async background callbacks (Celery and Diskcache managers) when the callback raises `PreventUpdate` or another exception before the variable is assigned.
 - [#3819](https://github.com/plotly/dash/pull/3819) Fix `RuntimeError: No active request in context` when a non-Dash path falls through to the FastAPI catch-all route. Fixes [#3812](https://github.com/plotly/dash/issues/3812).
 - [#3838](https://github.com/plotly/dash/pull/3838) Replace `mcp` dependency with inline types.

dash/testing/browser.py

@@ -629,10 +629,10 @@ def get_logs(self):
                 if entry["timestamp"] > self._last_ts
             ]
         warnings.warn(
-            "get_logs always return None with webdrivers other than Chrome",
+            "get_logs always return [] with webdrivers other than Chrome",
             stacklevel=2,
         )
-        return None
+        return []
 
     def reset_log_timestamp(self):
         """reset_log_timestamp only work with chrome webdriver."""