The main repo to test is AbstractPlotting/test/ReferenceTests; all backends use this to do integration tests with AbstractPlotting. There are several environment variables which govern the behaviour of the test suite.
Makie goes with the design of backends overloading the functions like
scatter(::Backend, args...), which means they can be loaded in by Julia's normal code loading mechanisms, and should be precompile-safe. Makie also tries to be statically compilable, but this isn't as straightforward as one could think. So far it seems that all kind of globals are not save for static compilation and generated functions seem to also make problems. I'm slowly removing problematic constructs from the dependencies and try to get static compilation as quick as possible.
Makie is statically compilable.
Check out this project for planned features and additions to Makie, as well as backlogged documentation issues.
If you're planning to add a new camera type, you will also have to edit the
apply_camera! function, to accept your camera type.