test(unit): refine TableWidget deadlock test style

- Refactored test_navigation_to_invalid_page_resets_to_valid_page_without_deadlock to follow established project conventions.
- Use internal import from bigframes.display.anywidget.
- Employ bigframes.option_context for setting widget state.
- Improved docstring to follow behavior-driven (Given/When/Then) style.

Author: shuoweil

tests/unit/display/test_anywidget.py

@@ -18,58 +18,58 @@
 import pandas as pd
 import pytest
 
-import bigframes.dataframe
+import bigframes
 
 # Skip if anywidget/traitlets not installed, though they should be in the dev env
 pytest.importorskip("anywidget")
 pytest.importorskip("traitlets")
 
 
-class TestTableWidget:
-    def test_navigation_to_invalid_page_resets_to_valid_page_without_deadlock(self):
-        """
-        Verifies that navigating to an invalid page resets to a valid page without deadlock.
+def test_navigation_to_invalid_page_resets_to_valid_page_without_deadlock():
+    """
+    Given a widget on a page beyond available data, when navigating,
+    then it should reset to the last valid page without deadlock.
+    """
+    from bigframes.display.anywidget import TableWidget
 
-        This behavior relies on _set_table_html releasing the lock before updating self.page,
-        preventing re-entrancy issues where the observer triggers a new update on the same thread.
-        """
-        from bigframes.display import TableWidget
+    mock_df = mock.create_autospec(bigframes.dataframe.DataFrame, instance=True)
+    mock_df.columns = ["col1"]
+    mock_df.dtypes = {"col1": "object"}
 
-        mock_df = mock.create_autospec(bigframes.dataframe.DataFrame, instance=True)
-        mock_df.columns = ["col1"]
-        mock_df.dtypes = {"col1": "object"}
+    mock_block = mock.Mock()
+    mock_block.has_index = False
+    mock_df._block = mock_block
 
-        mock_block = mock.Mock()
-        mock_block.has_index = False
-        mock_df._block = mock_block
-
-        # We mock _initial_load to avoid complex setup
-        with mock.patch.object(TableWidget, "_initial_load"):
+    # We mock _initial_load to avoid complex setup
+    with mock.patch.object(TableWidget, "_initial_load"):
+        with bigframes.option_context(
+            "display.repr_mode", "anywidget", "display.max_rows", 10
+        ):
             widget = TableWidget(mock_df)
 
-        # Simulate "loaded data but unknown total rows" state
-        widget.page_size = 10
-        widget.row_count = None
-        widget._all_data_loaded = True
+    # Simulate "loaded data but unknown total rows" state
+    widget.page_size = 10
+    widget.row_count = None
+    widget._all_data_loaded = True
 
-        # Populate cache with 1 page of data (10 rows). Page 0 is valid, page 1+ are invalid.
-        widget._cached_batches = [pd.DataFrame({"col1": range(10)})]
+    # Populate cache with 1 page of data (10 rows). Page 0 is valid, page 1+ are invalid.
+    widget._cached_batches = [pd.DataFrame({"col1": range(10)})]
 
-        # Mark initial load as complete so observers fire
-        widget._initial_load_complete = True
+    # Mark initial load as complete so observers fire
+    widget._initial_load_complete = True
 
-        # Setup timeout to fail fast if deadlock occurs
-        def handler(signum, frame):
-            raise TimeoutError("Deadlock detected!")
+    # Setup timeout to fail fast if deadlock occurs
+    def handler(signum, frame):
+        raise TimeoutError("Deadlock detected!")
 
-        signal.signal(signal.SIGALRM, handler)
-        signal.alarm(2)  # 2 seconds timeout
+    signal.signal(signal.SIGALRM, handler)
+    signal.alarm(2)  # 2 seconds timeout
 
-        try:
-            # Trigger navigation to page 5 (invalid), which should reset to page 0
-            widget.page = 5
+    try:
+        # Trigger navigation to page 5 (invalid), which should reset to page 0
+        widget.page = 5
 
-            assert widget.page == 0
+        assert widget.page == 0
 
-        finally:
-            signal.alarm(0)
+    finally:
+        signal.alarm(0)