I want to compare design screens to app development builds for pixel perfection. Is there any tool to do this?
If you are developing for iOS there's a library for that: https://github.com/facebook/ios-snapshot-test-case
Take screenshots on the iPhone, compare them with your designs.
I don't really have a solution to this, but I want to spitball some possibilities if anyone else is interested. Sketch 43's file format allows you to read the position of elements, their widths, heights, colors, etc.
Just going with React Native, for the time being, it should be possible to use something like Airbnb's React-Sketch to figure out where elements are being rendered in the viewport, what properties those elements have, and compare those results with the artboards from mocks created in Sketch at least if a React-Sketch like tool came around with larger support for primitives.
I would assume that this proposed tool would require some work on the designer's side (what objects and which of those objects' properties is relevant to QA), and on the developer's side (what components are related to the objects the designer said was important).
It'd be cool if you could do that for iOS and Android too.
Then the next obvious step is to build another app where you set your source sketch file as a "master" and the rendered one as a "copy".
You run it and it highlights the differences for you - that should be relatively easy at that point.
Check out Zeplin - helpful for designer-dev hand-offs, and also helpful from a testing standpoint as well!
Zeplin helps in the design to engineering flow, but he's asking about how to do QA design on existing engineering builds.
I'd recommend to use Android Studio and Xcode and run builds locally to do design QA. Depending how your release / staging environment is setup you might have to ask for those builds directly to the engineers. Once you have the builds, you can run them in the respective simulators and check for design inconsistencies (you can screenshot directly from simulator, or use the overlay feature in Zeplin..).
This is exactly what I am doing in my current workflow! Only once you have the builds you can check and be sure about design flaws!
If you are running the app in iOS Simulator you can use Uber Layer