Allow Dusk to assert environment matches Browser environment

DuskAssertBrowserEnvironment

<?php

namespace Tests;

use PHPUnit\Framework\Assert as PHPUnit;
use Laravel\Dusk\Browser as DuskBrowser;

class Browser extends DuskBrowser {

    /**
     * Check if the Browser environment matches with the
     * environment loaded by `php artisan dusk`
     * @return $this
     */
    public function assertBrowserEnvironment() {
        $environment = getenv('APP_ENV');
        $browserEnvironment = $this->visit('/_dusk/env')
            ->element('')->getText();

        PHPUnit::assertEquals($environment, $browserEnvironment,
            "Browser environment [{$browserEnvironment}] 
            diverge from the given environment [{$environment}]");

        return $this;
    }

}