* Add a test which demonstrates how no mutations are generated when an element is created & destroyed in the same 'cycle' (a cylce here being enforced by freezePage)
* Test demonstrating current behaviour I'm about to modify; the data-test="x" attribute is present twice in the mutation, as is the textContent value of 'y'
* Attribute or text modifications on just-added nodes are redundant as demonstrated in test case
* Some correct test changes from other tests; I've manually inspected each of these mutation removals and confirmed that the attribute values are already present in the newly added nodes elsewhere in the same mutation
* Improve reliability of test case as per Justin's advice
b4288791bd