I've been embracing Test-Driven Development (TDD) recently and it's had wonderful impacts on my development output and the resiliency of my codebase. I would like to extend this approach to some of the rendering work that I do in OpenGL, but I've been unable to find any good approaches to this.
I'll start with a concrete example so we know what kinds of things I want to test; lets say I want to create a unit cube that rotates about some axis, and that I want to ensure that, for some number of frames, each frame is rendered correctly.
How can I create an automated test case for this? Preferably, I'd even be able to write a test case before writing any code to render the cube (per usual TDD practices.) Among many other things, I'd want to make sure that the cube's size, location, and orientation are correct in each rendered frame. I may even want to make sure that the lighting equations in my shaders are correct in each frame.
The only remotely useful approach to this that I've come across involves comparing rendered output to a reference output, which generally precludes TDD practice, and is very cumbersome.
I could go on about other desired requirements, but I'm afraid the ones I've listed already are out of reach.
Answer
This seems like a good application of the Approval Tests framework or something like it.
As stated in the comments, you are still going to have an issue with false positives, if you happen to approve bad output, but this will at LEAST tell you when output has changed significantly.
Since you are using OpenGL, I'm assuming that approvals won't work for you directly, but the idea is sound. Just check the file hash and if it is different, show the failure in an appropriate diff viewer (like an image diff program). If you approve of the new version, update the "approved" file to match the new result.
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