[FEATURE] Expand testing

[vintagepc]

Describe the solution you'd like
Expand the automated testing to cover more of the code.

Just start simple with something that runs on a system with GL, deal with the headless build runners later... PPM seems like a nice convenient format.

It should:

• exercise the GL draw code
  AND
• take snapshots?
• Compare them to a reference?
  OR
• Inspect key pixels to make sure the visual looks like it should. May be easier with some drawables than others.
  OR
• Maybe intercept the GL calls for things like characters rendered to screen?

Additional context
Useful links for automated GL testing...
https://github.com/openrndr/setup-opengl

https://github.com/cirosantilli/cpp-cheat/blob/70b22ac36f92e93c94f951edb8b5af7947546525/opengl/offscreen.c

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glReadPixels.xhtml

https://github.com/mesa3d/piglit

https://pdiff.sourceforge.net/

[vintagepc]

Looks like EGL is required to run headless on the build server without opening a window... GLUT needs one.

[vintagepc]

@DRracer This one (and the upcoming associated PR, #231) should be of particular interest to you, it adds and makes use of extensive scripting and verification capability for components, telemetry, and tests. So while it serves as unit tests for the simulator, it should be more than suited to automated evaluation of firmware behaviour prior to release!

[DRracer]

@vintagepc well done, making a note for the upcoming FW release - we'll try it. Thanks for notifying me.