test(anywidget): Add tests for dark mode

Author: shuoweil

tests/js/table_widget.test.js

@@ -241,6 +241,49 @@ describe("TableWidget", () => {
 		});
 	});
 
+	describe("Theme detection", () => {
+		beforeEach(() => {
+			jest.useFakeTimers();
+			// Mock the initial state for theme detection tests
+			model.get.mockImplementation((property) => {
+				if (property === "table_html") {
+					return "";
+				}
+				if (property === "row_count") {
+					return 100;
+				}
+				if (property === "error_message") {
+					return null;
+				}
+				if (property === "page_size") {
+					return 10;
+				}
+				if (property === "page") {
+					return 0;
+				}
+				return null;
+			});
+		});
+
+		afterEach(() => {
+			jest.useRealTimers();
+			document.body.classList.remove("vscode-dark");
+		});
+
+		it("should add bigframes-dark-mode class in dark mode", () => {
+			document.body.classList.add("vscode-dark");
+			render({ model, el });
+			jest.runAllTimers();
+			expect(el.classList.contains("bigframes-dark-mode")).toBe(true);
+		});
+
+		it("should not add bigframes-dark-mode class in light mode", () => {
+			render({ model, el });
+			jest.runAllTimers();
+			expect(el.classList.contains("bigframes-dark-mode")).toBe(false);
+		});
+	});
+
 	it("should render the series as a table with an index and one value column", () => {
 		// Mock the initial state
 		model.get.mockImplementation((property) => {

tests/unit/display/test_anywidget.py

@@ -80,6 +80,24 @@ def handler(signum, frame):
             signal.alarm(0)
 
 
+def test_css_contains_dark_mode_media_query():
+    from bigframes.display.anywidget import TableWidget
+
+    mock_df = mock.create_autospec(bigframes.dataframe.DataFrame, instance=True)
+    # mock_df.columns and mock_df.dtypes are needed for __init__
+    mock_df.columns = ["col1"]
+    mock_df.dtypes = {"col1": "object"}
+
+    # Mock _block to avoid AttributeError during _set_table_html
+    mock_block = mock.Mock()
+    mock_block.has_index = False
+    mock_df._block = mock_block
+
+    with mock.patch.object(TableWidget, "_initial_load"):
+        widget = TableWidget(mock_df)
+        assert "@media (prefers-color-scheme: dark)" in widget._css
+
+
 @pytest.fixture
 def mock_df():
     df = mock.create_autospec(bigframes.dataframe.DataFrame, instance=True)