Need help with Fixture

Yii 2.0 Testing
1

I tried looking for answer in forum and google but none answer my question directly, and i need help desperately to get my unit test with Fixtures running, so here am i with my code snippet seeking help from experts here:

namespace common\tests\unit\provider;

use Yii;
use \common\models\provider\ProviderCalculation;
use \common\tests\fixtures\CompanyFixture;
use \common\tests\fixtures\ProviderFixture;

class ProviderCalculationTest extends \Codeception\Test\Unit
{
use \Codeception\Specify;

public function _fixtures()
{        
    return [
        'company' => [
            'class' => CompanyFixture::className(),
            // fixture data located in tests/_data/company.php
            'dataFile' => codecept_data_dir() .'company.php'
        ],            
        'provider' => [
            'class' => ProviderFixture::className(),                
            'dataFile' => codecept_data_dir() . 'provider.php'
        ],
    ];
}

public function _before()
{                          
}

public function _after()
{
}

public function testProviderCalculation(UnitTester $I){
    $this->specify("Provider calculation is wrong", function() {
        $providerCalculation = new ProviderCalculation(); 

        $companyType = $I->grabFixture('Provider', 'accrualOnly');                     
        //codecept_debug($companyLeaveType);            
        $calculated_value = $providerCalculation->getAccrualProduct(
            $companyType
        );
        $expected_value = 14;
        $this->assertEquals($expected_value, $calculated_value);
        
    });
}

}`

Everytime i run the test it gives me this error:

[yii\base\ErrorException] Argument 1 passed to common\tests\unit\leave\ProviderCalculationTest::testProviderCalculation() must be an instance of common\tests\unit\leave\UnitTester, none given

where have i done wrong?