Require at least one frontend and one backend

mopidy/utils/settings.py

@@ -143,6 +143,11 @@ def validate_settings(defaults, settings):
         'SPOTIFY_LIB_CACHE': 'SPOTIFY_CACHE_PATH',
     }
 
+    list_of_one_or_more = [
+        'BACKENDS',
+        'FRONTENDS',
+    ]
+
     for setting, value in settings.iteritems():
         if setting in changed:
             if changed[setting] is None:
@@ -167,6 +172,10 @@ def validate_settings(defaults, settings):
                 u'Deprecated setting, please set the value via the GStreamer '
                 u'bin in OUTPUT.')
 
+        elif setting in list_of_one_or_more:
+            if not value:
+                errors[setting] = u'Must contain at least one value.'
+
         elif setting not in defaults:
             errors[setting] = u'Unknown setting.'
             suggestion = did_you_mean(setting, defaults)

tests/utils/settings_test.py

@@ -9,6 +9,8 @@ from tests import unittest
 class ValidateSettingsTest(unittest.TestCase):
     def setUp(self):
         self.defaults = {
+            'BACKENDS': ['a'],
+            'FRONTENDS': ['a'],
             'MPD_SERVER_HOSTNAME': '::',
             'MPD_SERVER_PORT': 6600,
             'SPOTIFY_BITRATE': 160,
@@ -66,6 +68,18 @@ class ValidateSettingsTest(unittest.TestCase):
             'SPOTIFY_USERNAME', None)
         self.assertEqual(None, not_secret)
 
+    def test_empty_frontends_list_returns_error(self):
+        result = setting_utils.validate_settings(
+            self.defaults, {'FRONTENDS': []})
+        self.assertEqual(
+            result['FRONTENDS'], u'Must contain at least one value.')
+
+    def test_empty_backends_list_returns_error(self):
+        result = setting_utils.validate_settings(
+            self.defaults, {'BACKENDS': []})
+        self.assertEqual(
+            result['BACKENDS'], u'Must contain at least one value.')
+
 
 class SettingsProxyTest(unittest.TestCase):
     def setUp(self):