Add replaygain test for command backend

.travis.yml

@@ -23,6 +23,7 @@ install:
         travis_retry sudo apt-get install -qq
         bash-completion python-gi gir1.2-gstreamer-1.0
         gstreamer1.0-plugins-good gstreamer1.0-plugins-bad
+        mp3gain
     - travis_retry pip install tox sphinx
     - "[[ $TOX_ENV == 'py27' ]] && pip install coveralls || true"
 

test/test_replaygain.py

@@ -28,11 +28,11 @@ from beets.library import Item, Album
 from beets.mediafile import MediaFile
 
 
-class ReplayGainGstCliTest(unittest.TestCase):
+class ReplayGainCliTestBase(object):
 
     def setUp(self):
         self.setupBeets()
-        self.config['replaygain']['backend'] = u'gstreamer'
+        self.config['replaygain']['backend'] = self.backend
         self.config['plugins'] = ['replaygain']
         self.setupLibrary(2)
 
@@ -142,6 +142,14 @@ class ReplayGainGstCliTest(unittest.TestCase):
         self.assertNotEqual(max(peaks), 0.0)
 
 
+class ReplayGainGstCliTest(ReplayGainCliTestBase, unittest.TestCase):
+    backend = u'gstreamer'
+
+
+class ReplayGainCmdCliTest(ReplayGainCliTestBase, unittest.TestCase):
+    backend = u'command'
+
+
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)