check correctness of get_preferred_songs function

backend/experiment/rules/musical_preferences.py

@@ -284,11 +284,11 @@ def feedback_info(self):
         return info
 
     def get_preferred_songs(self, result_set, n=5):
-        top_songs = result_set.values('section').annotate(
-            avg_score=Avg('score')).order_by('-score')[:n]
+        top_results = result_set.annotate(
+            avg_score=Avg('score')).order_by('score')[:n]
         out_list = []
-        for s in top_songs:
-            section = Section.objects.get(pk=s.get('section'))
+        for result in top_results.all():
+            section = Section.objects.get(pk=result.section.id)
             out_list.append({'artist': section.song.artist,
                             'name': section.song.name})
         return out_list

backend/experiment/rules/tests/test_musical_preferences.py

@@ -0,0 +1,47 @@
+from django.test import TestCase
+from django.db.models import Avg
+
+from experiment.rules.musical_preferences import MusicalPreferences
+
+from experiment.models import Experiment
+from participant.models import Participant
+from result.models import Result
+from section.models import Playlist
+from session.models import Session
+
+class MusicalPreferencesTest(TestCase):
+    fixtures = ['playlist', 'experiment']
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.participant = Participant.objects.create()
+        cls.playlist = Playlist.objects.create(name='MusicalPrefences')
+        csv = ("SuperArtist,SuperSong,0.0,10.0,bat/artist1.mp3,0,0,0\n"
+               "SuperArtist,MehSong,0.0,10.0,bat/artist2.mp3,0,0,0\n"
+               "MehArtist,MehSong,0.0,10.0,bat/artist3.mp3,0,0,0\n"
+               "AwfulArtist,MehSong,0.0,10.0,bat/artist4.mp3,0,0,0\n"
+               "AwfulArtist,AwfulSong,0.0,10.0,bat/artist5.mp3,0,0,0\n")
+        cls.playlist.csv = csv
+        cls.playlist.update_sections()
+        cls.experiment = Experiment.objects.create(name='MusicalPreferences', rounds=5)
+        cls.session = Session.objects.create(
+            experiment=cls.experiment,
+            participant=cls.participant,
+            playlist=cls.playlist
+        )
+
+    def test_preferred_songs(self):
+        for index, section in enumerate(list(self.playlist.section_set.all())):
+            Result.objects.create(
+                question_key='like_song',
+                score=5-index,
+                section=section,
+                session=self.session
+            )
+        mp = MusicalPreferences()
+        preferred_sections = mp.get_preferred_songs(
+            self.session.result_set.order_by('?'), 3)
+        assert preferred_sections[0]['artist'] == 'SuperArtist'
+        assert preferred_sections[1]['name'] == 'MehSong'
+        assert preferred_sections[2]['artist'] == 'MehArtist'
+        assert 'AwfulArtist' not in [p['artist'] for p in preferred_sections]