Add automated tests for prev/next buttons on tabTest.js

[luixxiul]

Description

Add automated tests to tabTest.js for prev/next buttons on the tabs bar.

browser-laptop/app/renderer/components/tabs/tabs.js

Lines 172 to 176 in 9e6642f

	this.props.onPreviousPage
	? <span
	className='prevTab fa fa-caret-left'
	onClick={this.onPrevPage} />
	: null

browser-laptop/app/renderer/components/tabs/tabs.js

Lines 189 to 193 in 9e6642f

	this.props.onNextPage
	? <span
	className='nextTab fa fa-caret-right'
	onClick={this.onNextPage} />
	: null

Steps to Reproduce

1. Run npm run test -- --grep='tab tests'

Actual result:

It is not tested whether the prex/next buttons work properly.

Expected result:

The buttons should be tested that:

• They can be clicked
• Clicking them would switch tab pages
• Changing the value on about:preferences#tabs would show/hide them
• Closing the last tab on a tab page would open the existing tab page (blank tab page should not appear)
• Tabs, tabs' title and favicon would be re-rendered

etc.

Reproduces how often: [What percentage of the time does it reproduce?]

Additional Information

The span was replaced with browserButton locally. See: #11272

[luixxiul]

CC @cezaraugusto