Prototypes and interactive testing
Application prototype building is best started at a mid-resolution stage (post wireframe) where team members and other end user testers can find flaws in the interactivity of the product.
As a designer it is common to build in isolation and make assumptions that the user interface is intuitive and easy to use and therefore it is best to start testing as early as possible. As feedback is gathered the resolution of the prototype is refined until the finished artwork can be pushed to the frontend developers.
Preferring a lean and agile approach to digital product development I prefer a fast prototyping tool which can be shared across teams and multiple devices quickly for feedback and fits into the design work flow.
Both Adobe XD (just out of Beta at the time of writing) and Invisionapp offer a fast shareable tool for rapid prototyping applications across teams – although may not offer the full feature set that a more advanced tool like Axure RP