SignupCept.php

<?php
class SignUpHelper {

    /**
     * @var AcceptanceTester
     */
    private $tester;

    function __construct(AcceptanceTester $tester)
    {
        $this->tester = $tester;
    }

    public function signUp()
    {
        $I->wantTo('sign up');
        $I->amOnPage('/');
        $I->click('Sign up');
        $I->submitForm('#sign_up', [
            'first_name' => 'Joe',
            'last_name' => 'Jones',
            'email' => 'joe@jones.com',
            'password' => '1234',
            'password_confirmation' => '1234'
        ]);
        $I->amOnPage('/');
    }
}

$I = new AcceptanceTester($scenario);
$tester = new SignUpHelper($I);
$tester->signUp();