Add arrowLeft and arrowRight test suites
Add arrowLeft and arrowRight test suites

Added test suites for the `.arrowLeft()` and `.arrowRight()` methods of
the TextElement class. Also made some small changes/improvments to the
HTMLArea mock used in the TextElement class test spec.

ericcornelissen/htmlarea,ericcornelissen/htmlarea,ericcornelissen/html-area