yii2 unit testing having error of call to a member function getDb() on null
<pre><code>&lt;?php

namespace tests\codeception\engine;

use engine\components\BaseException;

use engine\components\BaseService;

use engine\modules\account\models\AccUser;

use engine\modules\account\models\AccUserActivity;

use engine\modules\account\services\AccountService;

use yii\db\Connection;



class AccountServiceTest extends \Codeception\TestCase\Test

{

    protected $tester;

    protected function _before()
    {
    }

    protected function _after()
    {
    }

    public function getDb()
    {
        $connection=Yii::$app-&gt;getDb();
    }

    public function testIsEmailAvailable()
    {
        $account = AccountService::model();


        // 1. Existing email check
        $email = 'alk@gmail.com';
        $this-&gt;assertEquals(true, $account-&gt;isEmailAvailable($email));

        // 2. New email check
        $email = 'arulvel@gmail.com';
        $this-&gt;assertEquals(false, $account-&gt;isEmailAvailable($email));

        // 3. Not an email check only character
        $email = 'arulvel';
        $this-&gt;assertEquals(false, $account-&gt;isEmailAvailable($email));

        // 4. Not an email check only numbers
        $email = '549876315';
        $this-&gt;assertEquals(false, $account-&gt;isEmailAvailable($email));

        // 5. Empty check
        $email = '';
        $this-&gt;assertEquals(false, $account-&gt;isEmailAvailable($email));

        return true;
    }

}
</code></pre>

<p>while running the test it showing an error like this</p>

<p>Trying to test is email available (AccountServiceTest::testIsEmailAvailable)... </p>

<p>PHP Fatal error:  Call to a member function getDb() on null in </p>

<p>/var/www/html/rewards/shopsup-rewards-</p>

<p>web/htdocs/vendor/yiisoft/yii2/db/ActiveRecord.php on line 133</p>

<p>FATAL ERROR. TESTS NOT FINISHED.
Call to a member function getDb() on null </p>

<p>when accessing that ActiveRecord.php on line 133 it is like</p>

<p><a href="http://i.stack.imgur.com/eMiHV.png" rel="nofollow">enter image description here</a></p>

<p>is there any configuration need to be made??</p>