Fatal error: Call to undefined function get_instance() about ci-phpunit-test HOT 5 CLOSED

$ composer create-project kenjis/codeigniter-composer-installer codeigniter
  - Installing codeigniter/framework (3.0.2)
$ cd codeigniter
$ composer require kenjis/ci-phpunit-test --dev
  - Installing kenjis/ci-phpunit-test (v0.8.2)
$ php vendor/kenjis/ci-phpunit-test/install.php

$ cd application/tests/
$ phpunit
PHPUnit 4.7.7 by Sebastian Bergmann and contributors.

...

Time: 809 ms, Memory: 5.50Mb

OK (3 tests, 3 assertions)

1) Manageuser_model_test::test_get_all_user
Error: Call to undefined function get_instance()

C:\xampp\htdocs\simaungv4\application\tests\models\Manageuser_model_test.php:7

<?php

use PHPUnit\Framework\TestCase;

class Manageuser_model_test extends TestCase {
    public function setup():void {
        $this->CI =& get_instance();
        $this->CI->load->model('manageuser_model');
        $this->obj = $this->CI->Manageuser_model;
    }

    public function test_get_all_user() {
  		$expected = [
  			1 => 'Fakultas',
  			2 => 'UPT',
  			3 => 'Prodi',
  		];
  		$user = $this->obj->get_all_user();
  		foreach ($user as $user_name) {
  			$this->assertEquals($expected[$user_name->user_id], $user_name->username);
  		}
	  }
}