completed library and test files

beets/mediafile.py

@@ -1643,6 +1643,12 @@ class MediaFile(object):
         StorageStyle('COMPOSERSORT'),
         ASFStorageStyle('WM/Composersortorder'),
     )
+    work = MediaField(
+        MP3DescStorageStyle(u'Work'),
+        MP4StorageStyle('----:com.apple.iTunes:Work'),
+        StorageStyle('WORK'),
+        ASFStorageStyle('beets/Work'),
+    )
     arranger = MediaField(
         MP3PeopleStorageStyle('TIPL', involvement='arranger'),
         MP4StorageStyle('----:com.apple.iTunes:Arranger'),

test/_common.py

@@ -70,6 +70,9 @@ def item(lib=None):
         composer=u'the composer',
         arranger=u'the arranger',
         grouping=u'the grouping',
+        work=u'the work title',
+        work_id=u'the work musicbrainz id',
+        work_disambig=u'the work disambiguation',
         year=1,
         month=2,
         day=3,

test/test_mediafile.py

@@ -352,6 +352,7 @@ class ReadWriteTestBase(ArtTestMixin, GenreListTestMixin,
         'lyricist',
         'composer',
         'composer_sort',
+        'work',
         'arranger',
         'grouping',
         'year',