Add notebook test for CSS loader

aiidalab_widgets_base/static/styles/global.css

@@ -0,0 +1,3 @@
+.for-testing-purposes {
+    color: red;
+}

notebooks/test.ipynb

@@ -0,0 +1,56 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import ipywidgets as ipw"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from aiida import load_profile\n",
+    "\n",
+    "load_profile();"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "label = ipw.Label(\"Testing\")\n",
+    "label.add_class(\"for-testing-purposes\")\n",
+    "display(label)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "base",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.13"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

tests_notebooks/test_notebooks.py

@@ -4,6 +4,17 @@
 from selenium.webdriver.common.by import By
 from selenium.webdriver.common.keys import Keys
 
+from aiidalab_widgets_base.utils.loaders import load_css_stylesheet
+
+
+def test_load_css_stylesheet(selenium_driver):
+    """Test `load_css_stylesheet` function."""
+    driver = selenium_driver("notebooks/test.ipynb")
+    package = "aiidalab_widgets_base.static.styles"
+    load_css_stylesheet(package=package, filename="global.css")
+    element = driver.find_element(By.CLASS_NAME, "for-testing-purposes")
+    assert element.value_of_css_property("color") == "red"
+
 
 def test_notebook_service_available(notebook_service):
     url, token = notebook_service