Hi, be patience I'm quite new at unit test in laravel I've this migrations

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class AddFieldsUsers extends Migration {

    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up() 
    {
        Schema::table('users', function(Blueprint $table)
        {
            $table->string('fullname');
            $table->string('username')->unique();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down() 
    {
        Schema::table('users', function(Blueprint $table) 
        {
            $table->dropColumn(array('fullname', 'username'));
        });
    }

}

and this test

/**
 * Class TestCase
 */
class TestCase extends Illuminate\Foundation\Testing\TestCase
{
    /**
     * @var bool
     */
    protected $useDatabase = true;

    /**
     * @var string
     */
    protected $userEmail = 'user@user.com';

    /**
     * @var string
     */
    protected $adminEmail = 'admin@admin.com';

    /**
     * Creates the application.
     *
     * @return Symfony\Component\HttpKernel\HttpKernelInterface
     */
    public function createApplication()
    {
        $unitTesting = true;

        $testEnvironment = 'testing';

        return require __DIR__ . '/../../bootstrap/start.php';
    }

    /**
     * Set up function for all tests
     *
     */
    public function setUp()
    {
        parent::setUp();

        if ($this->useDatabase) {
            $this->setUpDb();
            $this->createSentryUsersAndGroups();
        }
        // To test auth, we must re-enable filters on the routes
        // By default, filters are disabled in testing
        Route::enableFilters();
    }

    /**
     * Tear down function for all tests
     *
     */
    public function teardown()
    {
        Sentry::logout();
        Session::flush();
    }

    /**
     * Set up the database for tests
     *
     */
    public function setUpDb()
    {
        Artisan::call('migrate');
    }

    /**
     * Tear down the database for tests
     *
     */
    public function teardownDb()
    {
        Artisan::call('migrate:reset');
    }
}

when I run phpunit I've got

1. ExampleTest::testBasicExample Illuminate\Database\QueryException: SQLSTATE[HY000]: General error: 1 Cannot add a NOT NULL column with default value NULL (SQL: alter table "users" add column "fullname" varchar not null)

What's wrong ?