Add notebook test for CSS loader

aiidalab_widgets_base/static/styles/test.css

@@ -0,0 +1,3 @@
+.for-testing-purposes {
+  color: rgb(255, 0, 0);
+}

notebooks/test.ipynb

@@ -0,0 +1,68 @@
+{
+ "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": [
+    "# DO NOT REMOVE!\n",
+    "# This triggers required jupyter-notebook specific actions.\n",
+    "# See `aiidalab_widgets_base.__init__.py` for details\n",
+    "import aiidalab_widgets_base"
+   ]
+  },
+  {
+   "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": "Python 3 (ipykernel)",
+   "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

@@ -5,6 +5,13 @@
 from selenium.webdriver.common.keys import Keys
 
 
+def test_load_css_stylesheet(selenium_driver):
+    """Test `load_css_stylesheet` function."""
+    driver = selenium_driver("notebooks/test.ipynb")
+    element = driver.find_element(By.CLASS_NAME, "for-testing-purposes")
+    assert element.value_of_css_property("color") == "rgba(255, 0, 0)"
+
+
 def test_notebook_service_available(notebook_service):
     url, token = notebook_service
     response = requests.get(f"{url}/?token={token}")