API, sharable: serialize users_shared_with

- Changes sharable serializers so that, when requested with
`keys=users_shared_with`, they return a list of encoded user ids for
each user that the item has been shared with
- Adds tests in test_HistoryManager

lib/galaxy/managers/sharable.py

@@ -335,7 +335,8 @@ def add_serializers( self ):
 
         self.serializers.update({
             'user_id'           : self.serialize_id,
-            'username_and_slug' : self.serialize_username_and_slug
+            'username_and_slug' : self.serialize_username_and_slug,
+            'users_shared_with' : self.serialize_users_shared_with
         })
         # these use the default serializer but must still be white-listed
         self.serializable_keyset.update([
@@ -357,9 +358,12 @@ def serialize_username_and_slug( self, item, key, **context ):
 
     # the only ones that needs any fns:
     #   user/user_id
-    #   user_shares?
     #   username_and_slug?
 
+    def serialize_users_shared_with( self, item, key, **context ):
+        share_assocs = self.manager.get_share_assocs( item )
+        return [ self.serialize_id( share, 'user_id' ) for share in share_assocs ]
+
 
 class SharableModelDeserializer( base.ModelDeserializer,
         taggable.TaggableDeserializerMixin, annotatable.AnnotatableDeserializerMixin, ratable.RatableDeserializerMixin ):

test/unit/managers/test_HistoryManager.py

@@ -437,6 +437,14 @@ def test_sharable( self ):
         serialized = self.history_serializer.serialize( history1, sharable_attrs )
         self.assertKeys( serialized, sharable_attrs )
 
+        self.log( 'should return user_id for user with whom it\'s been shared' )
+        non_owner = self.user_manager.create( **user3_data )
+        self.history_manager.share_with( history1, non_owner )
+        serialized = self.history_serializer.serialize( history1, [ 'users_shared_with' ] )
+        self.assertKeys( serialized, [ 'users_shared_with' ] )
+        self.assertIsInstance( serialized[ 'users_shared_with' ], list )
+        self.assertEqual( serialized[ 'users_shared_with' ][0], self.app.security.encode_id( non_owner.id ) )
+
     def test_purgable( self ):
         user2 = self.user_manager.create( **user2_data )
         history1 = self.history_manager.create( name='history1', user=user2 )