How to mock DB in CI?

[inandi]

PHPUnit 9.5.25 #StandWithUkraine
PHP 7.3.29 with Xdebug 3.0.0

How to mock this CI function with all DB codes as well

function update($sessionActiveUserId = null)
{
    $logTitle = "update usertype";
    $data = $methodResponseObj = array();
    try {
        array_walk($_POST, 'trim');
        foreach ($_POST as $k => $r) {
            if ($k === 'id') {
                ${$k} = base64_decode($r);
                $data[$k] = base64_decode($r);
            }
        }
        $this->db->where('id', $id);
        if ($this->db->update('tbl_demo', $data)) {
            $this->logArray[] = helperFunction($logTitle, $this->db->last_query());
            $methodResponseObj = array(
                'status' => true,
                'type' => W_STATUS_SUCCESS,
                'msg' => 'Usertype Updated Successfully.'
            );
        } else {
            $this->traitFunction1($logTitle);
        }
    } catch (Exception $e) {
        $methodResponseObj = $this->traitFunction2($e, $logTitle);
    }
    return $methodResponseObj;
}

I started to write test case but somehow I am lost not sure I am going in right direction

<?php

class Project_Model_Test extends TestCase
{

    /** @var Project_Model $modelObj */
    protected $modelObj;

    /** @var \CI_Model $CI */
    protected $CI;

    /** @var \CI_DB_mysqli_driver $dbMock */
    protected $dbMock;

    /**
     * Set up
     *
     * @return void
     */
    public function setUp(): void
    {
        $this->resetInstance();
        $this->CI->load->model('Project_Model');
        $this->modelObj = $this->CI->Project_Model;

        $this->dbMock = $this->getMockBuilder('CI_DB_query_builder')
            ->disableOriginalConstructor()
            ->getMock();
    }

    public function testUpdateUsertype()
    {
        $actual = $this->modelObj->update();

        // // Set up a mock database connection
        $dbMock = $this->getMockBuilder('CI_DB_query_builder')
            ->disableOriginalConstructor()
            ->getMock();

        // Expect the 'where' and 'update' methods to be called with specific arguments
        $dbMock->expects($this->once())
            ->method('where')
            ->with('id', base64_decode('example_id'))
            ->will($this->returnValue(false));
    }
}

Thanks is advance!!!

[kenjis]

See https://github.com/kenjis/ci-phpunit-test/blob/3.x/docs/HowToWriteTests.md#using-phpunit-mock-objects
and https://github.com/kenjis/ci-app-for-ci-phpunit-test/blob/3.x/application/tests/models/Category_model_mocking_db_test.php