Mock databases function from drupal 7 - drupal-7

Question

I want to create a phpunit test from the following code, but I'm not even sure if it worth it, because the code contains db_update and db_query functions, so, those are database functions and I don't know if it make sense create a test for this, because I don't know if should assume drupal code is working fine.
<?php
namespace Drupal\forum_innovation\Forum;
/**
* Created by PhpStorm.
* User: ldcontreras
* Date: 30/05/18
* Time: 18:26
*/
class ForumCounter implements ForumInterface {
public static function setForumCounter($forum, $uid) {
$counterState = db_update('forum_counter_states')
->fields(array(
'state' => 'read',
))
->condition('uid', $uid)
->condition('tid', $forum)
->execute();
return $counterState;
}
public static function getForumNotification($forum, $uid) {
$unReadNotifications =
db_query('SELECT count(*) as counter
FROM {forum_counter_states} as f WHERE f.uid = :uid AND f.state = :state AND f.tid = :forum',
array(
':uid' => $uid,
':forum' => $forum,
':state' => 'unread'
)
)->fetchAll();
return $unReadNotifications[0]->counter;
}
}
I'm trying to create a test like this, but I need some help and clarification:
<?php
/**
* Created by PhpStorm.
* User: ldcontreras
* Date: 8/06/18
* Time: 10:02
*/
namespace Drupal\forum_innovation\Forum;
class ForumCounterTest extends \PHPUnit_Framework_TestCase {
public function TestSetForumCounter() {
$db_query = $this->getMock('db_update', array('fields', 'condition', 'execute'));
$db_query->expects($this->once())->method('fields')->with($this->equalTo(array(':uid' => 3024));
$db_query->expects($this->once())->method('condition')->with($this->equalTo(array(':uid' => 3024)));
$db_query->expects($this->once())->method('condition')->with($this->equalTo(
array(':tid' => 83))->will(
$this->returnCallback('callback'));
}
}
Thanks!