Test join request serializer since without _id key in serializable hash it failed

spec/serializers/join_request_serializer_spec.rb

@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+describe JoinRequestSerializer do
+  it 'works' do
+    user = create :user
+    list = create :list
+    join_request = list.join_request_for_user(user)
+    JoinRequestSerializer.new(join_request).as_json.should == {
+      users: [UserUserSerializer.new(user).as_json(root: false)],
+      join_request: {
+        id: "jr-#{user.id}",
+        created_at: nil,
+        updated_at: nil,
+        list_id: list.id,
+        user_id: user.id
+      }
+    }
+  end
+end