`Node` ids, classes and queries allow us to focus ...

# tornadofx

[hastebrot]

Node ids, classes and queries allow us to focus on testing the behaviur rather than implementation details. we could even write a GUI test before the corresponding GUI code even exists.
@johnzeringue mentioned "This is consistent with BDD principles: implementation details aren't relevant in testing." in a PR on TestFX's github (https://github.com/TestFX/TestFX/pull/210).