[tests] Flagged tests that should not be run on production env

These tests depends on the static storage backend of the project.
In prod environment, the filenames could get changed due to
static minification and cache invalidation. Hence, these tests
should not be run on prod environment because they'll fail.

(cherry picked from commit b2079fa)

README.rst

@@ -186,6 +186,9 @@ Run tests with:
     # tests for the sample app
     SAMPLE_APP=1 ./runtests.py
 
+    # If you running tests on PROD environment
+    ./runtests.py --exclude skip_prod
+
 When running the last line of the previous example, the environment variable ``SAMPLE_APP`` activates
 the sample app in ``/tests/openwisp2/`` which is a simple django app that extends ``openwisp-notifications``
 with the sole purpose of testing its extensibility, for more information regarding this concept,

openwisp_notifications/tests/test_admin.py

@@ -6,7 +6,7 @@
 from django.contrib.auth.models import Permission
 from django.core.cache import cache
 from django.forms.widgets import MediaOrderConflictWarning
-from django.test import TestCase, override_settings
+from django.test import TestCase, override_settings, tag
 from django.urls import reverse
 
 from openwisp_notifications import settings as app_settings
@@ -113,13 +113,20 @@ def test_cached_invalidation(self):
         self.client.get(self._url)
         self.assertEqual(cache.get(cache_key), 1)
 
+    @tag('skip_prod')
+    # This tests depends on the static storage backend of the project.
+    # In prod environment, the filenames could get changed due to
+    # static minification and cache invalidation. Hence, these tests
+    # should not be run on prod environment because they'll fail.
     def test_default_notification_setting(self):
         res = self.client.get(self._url)
         self.assertContains(
             res, '/static/openwisp-notifications/audio/notification_bell.mp3'
         )
         self.assertContains(res, 'window.location')
 
+    @tag('skip_prod')
+    # For more info, look at TestAdmin.test_default_notification_setting
     @patch.object(
         app_settings,
         'OPENWISP_NOTIFICATIONS_SOUND',
@@ -233,6 +240,8 @@ def test_ignore_notification_widget_add_view(self):
         self.assertNotContains(response, 'owIsChangeForm')
 
 
+@tag('skip_prod')
+# For more info, look at TestAdmin.test_default_notification_setting
 class TestAdminMedia(BaseTestAdmin):
     """
     Tests notifications admin media