fix(belongs-to): create now returns target model (#9980)

lib/associations/belongs-to.js

@@ -221,15 +221,15 @@ class BelongsTo extends Association {
    *
    * @see {@link Model#create}  for a full explanation of options
    *
-   * @returns {Promise}
+   * @returns {Promise<Model>} The created target model
    */
   create(sourceInstance, values, options) {
     values = values || {};
     options = options || {};
 
     return this.target.create(values, options)
-      .then(newAssociatedObject =>
-        sourceInstance[this.accessors.set](newAssociatedObject, options)
+      .then(newAssociatedObject => sourceInstance[this.accessors.set](newAssociatedObject, options)
+        .then(() => newAssociatedObject)
       );
   }
 }

lib/associations/has-one.js

@@ -239,7 +239,7 @@ class HasOne extends Association {
    *
    * @see {@link Model#create} for a full explanation of options
    *
-   * @returns {Promise}
+   * @returns {Promise<Model>} The created target model
    */
   create(sourceInstance, values, options) {
     values = values || {};

test/integration/associations/belongs-to.test.js

@@ -412,11 +412,9 @@ describe(Support.getTestDialectTeaser('BelongsTo'), () => {
 
       return this.sequelize.sync({ force: true }).then(() => {
         return Task.create({ title: 'task' }).then(task => {
-          return task.createUser({ username: 'bob' }).then(() => {
-            return task.getUser().then(user => {
-              expect(user).not.to.be.null;
-              expect(user.username).to.equal('bob');
-            });
+          return task.createUser({ username: 'bob' }).then(user => {
+            expect(user).not.to.be.null;
+            expect(user.username).to.equal('bob');
           });
         });
       });