Adding Change Node tests

Tests to cover the Change Node. I didn't feel an urge to factor out the common helper.load() function this time as it's not quite as repetitive as in the case of the Switch Node. Please let me know if I shall add utility methods. I personally don't think it's necessary here.
I don't think the node should be doing this.... It's use of eval is bad and on the JSHint hit list.

Need to check what the expected behaviour is - leave this test out for now.