diff --git a/tests/core/test_mixer.py b/tests/core/test_mixer.py
index e3fa6be6..80e6f7ef 100644
--- a/tests/core/test_mixer.py
+++ b/tests/core/test_mixer.py
@@ -2,27 +2,34 @@ from __future__ import absolute_import, unicode_literals
 
 import unittest
 
-from mopidy import core
+import mock
+
+from mopidy import core, mixer
 
 
 class CoreMixerTest(unittest.TestCase):
     def setUp(self):  # noqa: N802
-        self.core = core.Core(mixer=None, backends=[])
+        self.mixer = mock.Mock(spec=mixer.Mixer)
+        self.core = core.Core(mixer=self.mixer, backends=[])
 
-    def test_volume(self):
-        self.assertEqual(self.core.mixer.get_volume(), None)
-
-        self.core.mixer.set_volume(30)
+    def test_get_volume(self):
+        self.mixer.get_volume.return_value.get.return_value = 30
 
         self.assertEqual(self.core.mixer.get_volume(), 30)
+        self.mixer.get_volume.assert_called_once_with()
 
-        self.core.mixer.set_volume(70)
+    def test_set_volume(self):
+        self.core.mixer.set_volume(30)
 
-        self.assertEqual(self.core.mixer.get_volume(), 70)
+        self.mixer.set_volume.assert_called_once_with(30)
 
-    def test_mute(self):
-        self.assertEqual(self.core.mixer.get_mute(), False)
-
-        self.core.mixer.set_mute(True)
+    def test_get_mute(self):
+        self.mixer.get_mute.return_value.get.return_value = True
 
         self.assertEqual(self.core.mixer.get_mute(), True)
+        self.mixer.get_mute.assert_called_once_with()
+
+    def test_set_mute(self):
+        self.core.mixer.set_mute(True)
+
+        self.mixer.set_mute.assert_called_once_with(True)