This issue should be tested in one device of each type. Navigate to a page with a text editor. Ie. new page on a wiki. Click on the bold button, check it's activated and write a bit. Check the text written is in bold. Click again on the bold button and check it's deactivated. Write and check the text written is not in bold. Now test again with italics, underline and strike buttons. On desktop. Also check that hovering over the buttons a caption is displayed describing the buttons.