Functional test in Yii2 with codeception get 404 error

My functional test file

<?php
namespace api\tests;
use api\tests\FunctionalTester;
use Yii;

class ExampleCest
{
    public function _before(FunctionalTester $I)
    {
    }

    public function _after(FunctionalTester $I)
    {
    }

    // tests
    public function tryToTest(FunctionalTester $I)
    {
        $I->sendGET('example/test2');
        $I->seeResponseCodeIs(200); // Unauthorized
        $I->seeResponseContains('test2');    
    }
}

I tried 2 different functional.suite.yml files to run the test:

// 1. functional.suite.yml, test run successfully:
    actor: FunctionalTester
    modules:
        enabled:
            - REST:
                url: http://api.xxxxx.local/v1/
                depends: PhpBrowser
                part: Json    
            - \api\tests\Helper\Functional


// 2. functional.suite.yml, test failed without setting defaultRoute in Yii configuration file, but succeed if I set `'defaultRoute' => 'v1/example/test2',`:
    actor: FunctionalTester
    modules:
        enabled:
            - REST:
                url: v1/
                depends: Yii2
                part: Json    
            - \api\tests\Helper\Functional        

The error message when failed:

ExampleCest: Try to test
Signature: api\tests\ExampleCest:tryToTest
Test: tests/functional/ExampleCest.php:tryToTest
Scenario --
 I send get "example/test2"
  [Request] GET v1/example/test2
  [Request Headers] []
  [yii\web\HttpException:404] 'yii\\base\\InvalidRouteException: Unable to resolve the request "". in /Applications/MAMP/htdocs/gaea/vendor/yiisoft/yii2/base/Module.php:537            

• Question 1: About the above 2 functional.suite.yml files, which is the right way to test rest api and why?
• Question 2: I have no idea why the 2nd functional.suite.yml file could be faied, since I can get right response in the browser from http://localhost/MYPROJECT/api/web/index.php?r=v1/example/test2.

My environment: Codeception: v2.3.8 Yii: v2.0.14 PHP: v7.0.26