Testing GC and finalizers

a) How is GC tested in Julia (read as: method)?
b) Where could i find test code (read as: where in the julia repo)?
c) Are there known tests for finalizers somewhere in packages?

For reference: you are asking because of this issue, right?

Not only. There is the pending https://github.com/JuliaGraphics/Cairo.jl/issues/215 and i had the feeling, that https://github.com/JuliaGraphics/Cairo.jl/issues/225 is somehow connected.