1891568 - Add unit tests for functionality of text and layout controls

Status: NEW

(Toolkit :: Reader Mode, enhancement)

Description

[Irene Ni]

At the moment, we only have unit test coverage for opening/closing the menu dropdown, but not the actual functionality of the controls. We want to add a set of unit tests that make sure that setting the text and layout properties result in the correct styling changes. The approach can be similar to the tests for setting color themes, where we set the pref to a certain value, load up a mock article in Reader View, and use getComputedStyle() to check if the custom css variable has the correct value.