laravel 5 codeceoption - Couldn't click Link or Button by name or CSS or XPath

I wrote a simple test in codeception and laravel 5,every time I run it with specify name like:

vendor/bin/codecept run functional SignUpCept

it works right but without SignUpCept it doesn't work. here is my code:

$I = new FunctionalTester($scenario);
$I->am('a guest');
$I->wantTo('Sign up for a larabook account');
$I->amOnPage('/');
$I->click('Sign Up!');

and this is a link in my view:

<a href="http://ift.tt/1iBXaP2?" class="btn btn-lg btn-primary">Sign Up!</a>

and the error message is:

Couldn't click "Sign Up!":
Link or Button by name or CSS or XPath 'Sign Up!' was not found on page.

Scenario Steps:
3. I click "Sign Up!"
2. I am on page "/"
1. As a a guest