feat(entity): prevent accidental infinite loops

fixed tests. server needs to return an id on saving.  since it'll make it too complicated to also return fake associated entity ids, the test got simplified there

build/tasks/server.js

@@ -14,7 +14,8 @@ app.all('*', function(req, res) {
     access_token: req.body.access_token,
     method: req.method,
     contentType: req.header('content-type'),
-    Authorization: req.header('Authorization')
+    Authorization: req.header('Authorization'),
+    id: 667
   });
 });
 

src/entity.js

@@ -171,6 +171,10 @@ export class Entity {
       if (!relation || relation.type !== 'entity') {
         // Many relation, create and then link.
         return entity.save().then(() => {
+          if (entity.isNew()) {
+            throw new Error('Entity did not return return an id on saving.');
+          }
+
           return this.addCollectionAssociation(entity, property);
         });
       }

test/entity.spec.js

@@ -236,13 +236,7 @@ describe('Entity', function() {
       });
 
       parentEntity.save().then(response => {
-        let idBar = response.bar.id;
-        let idParent = response.id;
-
-        expect(typeof idParent).toEqual('number');
-        expect(typeof idBar).toEqual('number');
-
-        expect(response).toEqual({bar: {baby: 'steps', id: idBar}, test: 'case', id: idParent});
+        expect(response.body).toEqual({bar: {baby: 'steps'}, test: 'case'});
         done();
       });
     });