title: What are the possible ways of testing visual parts of a WebGL/Canvas-based game
body: <p>Assuming a game written using Dart + WebGL/Canvas...</p>
  
  <p>Much of the logic, maths, input handling, etc. is easily testable with code; but ensuring you actually do the right thing to make your sprite turn up on screen at the correct location/orientation/etc. is more tricky.</p>
  
  <p>What tools/APIs exist that would assist testing the actual rendered output?</p>