Testing: class 'SQLite3' not found

I'm using CI 4.0 (latest).
I try testing using PHPUnit. installed offline, not using composer.

Using

Code:

ControllerTester

work for simple pages. But error (HTTP Exception) for page which requires logged in.

Using FeatureTestCase however, not work and says class 'SQLite3' not found. When I see trace result, it points to

PHP Code:

\system\Database\SQLite3\Connection.php:89: 'new \SQLite3($this->database)' 


.
This should be SQLite3 class from php extension because it has root namespace. Normal page using that class is working. Using PHPUnit on CI4.0 is not.

I just test using simple page using

PHP Code:

$db = new \SQLite3($path); 


is work.

How do i resolve this?