[FIX] theme_test_custo: add test for the mobile/desktop theme preview

With the Milk redesign in [1], the possibility to use the mobile/desktop
switcher on a theme preview to see how it behaves/displays on those
devices didn't work anymore.

It has been fixed in [2], but in order to prevent future breaks, this
commit tests this functionality.

task-3355253

[1]: https://github.com/odoo/odoo/commit/caef16ee4e5351142ef04f02798999ccb38a56bc
[2]: https://github.com/odoo/odoo/commit/9445f61bcaee88bc6ac2fc373d7eca4e4b38c154

closes odoo/design-themes#670

X-original-commit: ed2fdd45f2
Related: odoo/odoo#127911
Signed-off-by: Romain Derie (rde) <rde@odoo.com>

theme_test_custo/tests/test_theme_creation.py

@@ -2,7 +2,7 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from odoo.tests import HttpCase, tagged
-
+from odoo.addons.website.tests.test_configurator import TestConfiguratorCommon
 
 # TODO: `test_themes` tag should not be there, runbot config should be adapted
 #       to test this module too. There is a special config for the theme repo.
@@ -14,3 +14,8 @@ class Crawler(HttpCase):
         website.theme_id = theme_custo.id
         theme_custo.with_context(load_all_views=True, apply_new_theme=True)._theme_load(website)
         self.start_tour('/@/example', "theme_menu_hierarchies", login='admin')
+
+@tagged('post_install', '-at_install')
+class TestThemeConfigurator(TestConfiguratorCommon):
+    def test_website_theme_preview(self):
+        self.start_tour('/web#action=website.action_website_configuration', 'website_theme_preview', login="admin")