fix(curriculm): add user story and test for theme switcher (#66636)

Co-authored-by: Anna <a.rcottrill521@gmail.com>
Co-authored-by: sembauke <semboot699@gmail.com>

curriculum/challenges/english/blocks/lab-theme-switcher/687ad7be1ff45032ccf1d92f.md

@@ -33,6 +33,7 @@ In this lab, you will build an app that switches between different themes. When
 9. When the `#theme-dropdown` element is displayed, the `aria-expanded` attribute should be set to `"true"` for the `button` element.
 10. When the users clicks on the `#theme-switcher-button` while the `#theme-dropdown` element is displayed, the menu should be closed and the `hidden` attribute should be added and the `aria-expanded` attribute should be set to `"false"`.
 11. When a user clicks on the `#theme-switcher-button` and selects a theme, the corresponding `theme-<name>` class should be added to the `body` element and the related theme message you set in the `themes` array should display in the `aria-live="polite"` element. 
+12. When a user clicks on the `#theme-switcher-button` and selects a different theme than the current one, the `body` theme class and status message should update to match the new selection.
 
 # --before-all--
 
@@ -299,6 +300,29 @@ const selectedTheme = themes?.find(theme => theme.name === selectedThemeName);
 assert.equal(liveRegion?.textContent, selectedTheme?.message);
 ```
 
+When a user clicks on the `#theme-switcher-button` and selects two different themes, the `body` class and status message should update to match each selected theme.
+
+```js
+const liveRegion = document.querySelector('[aria-live="polite"]');
+const themeDropdownBtn = document.getElementById("theme-switcher-button");
+const listItems = document.querySelectorAll("#theme-dropdown li");
+
+themeDropdownBtn?.dispatchEvent(new Event("click"));
+listItems[0]?.dispatchEvent(new Event("click", { bubbles: true }));
+const firstClass = document.body.className;
+const firstMessage = liveRegion?.textContent;
+
+themeDropdownBtn?.dispatchEvent(new Event("click"));
+listItems[1]?.dispatchEvent(new Event("click", { bubbles: true }));
+const secondClass = document.body.className;
+const secondMessage = liveRegion?.textContent;
+
+assert.equal(firstClass, listItems[0]?.id);
+assert.equal(secondClass, listItems[1]?.id);
+assert.notEqual(firstClass, secondClass);
+assert.notEqual(firstMessage, secondMessage);
+```
+
 # --seed--
 
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