bokeh.object.PlotObject testing

Hey I’ve written a few tests for PlotObject but I’ve kind ending up going off track with them as PlotObject is kind of hard to pick apart with classes/metaclassing involved. I couldn’t find any solid examples of what the json input to it is supposed to look like. here’s the commit, I’m mostly just testing the behavior I see when I prod the various functions but things have started to go a bit awry! test_finalize and test_load_json feel like they are absolutely wrong and not testing expected behavior like they should be. Mostly I struggled to get a PlotObject set up correctly so calling finalize would actually work, in the end I gave up and cheesed it by overwriting some attributes!