Automated testing

[pablode]

Set up the testing infrastructure for..

• [ ] Unit tests
• [ ] File tests with..
  • [ ] Khronos's sample models
  • [ ] Khronos's validation models
  • [ ] Custom models
• [ ] Reference images

Some open questions are:

• do we put file tests in a separate repo?
• what reference renderer to use?
  • USD+MaterialX is barely supported; gatling could be used in the future