Tests should not depend on Matrix-nio, that uses lxml that needs a lot of dependencies and a lot of time to build

corres2math/settings.py

@@ -51,16 +51,14 @@ INSTALLED_APPS = [
     'django.forms',
 
     'bootstrap_datepicker_plus',
+    'cas_server',
     'crispy_forms',
-    'django_extensions',
     'django_tables2',
     'haystack',
     'logs',
-    'mailer',
     'polymorphic',
     'rest_framework',
     'rest_framework.authtoken',
-    'cas_server',
 
     'api',
     'eastereggs',
@@ -68,6 +66,12 @@ INSTALLED_APPS = [
     'participation',
 ]
 
+if "test" not in sys.argv:  # pragma: no cover
+    INSTALLED_APPS += [
+        'django_extensions',
+        'mailer',
+    ]
+
 MIDDLEWARE = [
     'django.middleware.security.SecurityMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',