PHPUnit in LAravel error : Exception' with message 'SQLSTATE[HY000] [2005] Unknown MySQL server host 'mysql' (2)'

I am trying to run PHPunit test for visit('/') in LAravel 5 but it fails with this message below : (my app is running in docker container http://www.spiralout.eu/2015/12/dockervel-laravel-development.html )

    class MyTest extends TestCase
{
    /**
     * A basic test example.
     *
     * @return void
     */
    public function testExample()
    {
        $this->assertTrue(true);
    }


        public function providerAllUrisWithResponseCode()
    {
        return [
            ['/', 200],
            ['/thank', 200],
            ['/non-existing', 404],
        ];
    }

        public function testDisplayThankYou($value='')
    {
        $this->visit('/thankyou')
        ->see('Thank you!');
    }       


        public function testPageControllerGet()
    {
        $this->call('GET', '/');
    }
        public function testDisplayWelcome($value='')
    {
        $this->visit('/')
        ->see('Welcome');

    }
}

and I am getting this error .

        $vendor/bin/phpunit 
PHPUnit 4.8.26 by Sebastian Bergmann and contributors.

...F

Time: 24.01 seconds, Memory: 16.00MB

There was 1 failure:

1) MyTest::testDisplayWelcome

A request to [http://localhost] failed. Received status code [500].

    ..vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/InteractsWithPages.php:196

    ..vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/InteractsWithPages.php:80
    ..vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/InteractsWithPages.php:61
    .../www/tests/ExampleTest.php:16

    Caused by
    exception 'PDOException' with message 'SQLSTATE[HY000] [2005] Unknown MySQL server host 'mysql' (2)' 
    in ../vendor/laravel/framework/src/Illuminate/Database/Connectors/Connector.php:55

My behat features passed ! My .env.* files look like :

.env
DB_CONNECTION=mysql
DB_HOST=mysql
DB_PORT=3306
DB_DATABASE=homestead
DB_USERNAME=homestead
DB_PASSWORD=secret

.env.behat
DB_CONNECTION=mysql
DB_HOST=127.0.0.1 
DB_PORT=3306
DB_DATABASE=homestead
DB_USERNAME=homestead
DB_PASSWORD=secret

Also : If I remove or change DB_HOST=127.0.0.1 in .env.behat and I run behat it returns an error!

The line 50 in Connector.php says :

   public function createConnection($dsn, array $config, array $options)
    {
**here it breaks**-->   $username = Arr::get($config, 'username');

        $password = Arr::get($config, 'password');

        try {
            $pdo = new PDO($dsn, $username, $password, $options);
        } catch (Exception $e) {
            $pdo = $this->tryAgainIfCausedByLostConnection(
                $e, $dsn, $username, $password, $options
            );
        }

        return $pdo;
    }

For example when I run DB ::table('something')->get(); it's working fine.

Someone sees the problem?