Add test for theme switching

Author: dkobylianskii

tests/test_tui.py

@@ -18,6 +18,20 @@ async def test_browse_plot() -> None:
         assert pilot.app.query_one("#main-view").current == "plot"
 
 
+async def test_theme_switch() -> None:
+    async with Browser(
+        skhep_testdata.data_path("uproot-Event.root")
+    ).run_test() as pilot:
+        await pilot.press("down", "down", "down", "enter")
+        browser_theme = pilot.app.theme
+        plot_theme = pilot.app.theme
+        await pilot.press("t")
+        new_browser_theme = pilot.app.theme
+        new_plot_theme = pilot.app.theme
+        assert browser_theme != new_browser_theme
+        assert plot_theme != new_plot_theme
+
+
 async def test_browse_empty() -> None:
     async with Browser(
         skhep_testdata.data_path("uproot-empty.root")