Adding tests for XML parser node

I couldn't find a way to exercise the two remaining error case lines which aren't covered by this pull request.

* If you try to create an invalid js object to force the error case on line 31 then the test doesn't compile. 
* I "think" the error case on line 45 is never exercised because any error from the parseString(...) method is handled on line 38. If this is the case then it should be removed.