LinkTest.php

<?php

namespace MySite\Tests;

use SilverStripe\Dev\SapphireTest;

/**
 * Class PageTest
 * @package MySite\Tests
 */
class PageTest extends SapphireTest
{
    /**
     * @var string
     */
    protected static $fixture_file = '';

    /**
     *
     */
    public function testLink()
    {
        $this->logInWithPermission('ADMIN');
        $page = \Page::create(['title' => 'Hello World', 'URLSegment' => 'hello-world']);
        $page->write();
        $page->publishRecursive();

        $expected = '/hello-world/';
        $actual = $page->Link(); //- actual is absolute path to webroot  /var/www/public/silverstripe4.dev

        $this->assertEquals($expected, $actual);
        $this->logOut();
    }
}