laravel 5.1 - phpUnit class cannot be converted into string exception

I am dabbling with PHPUnit that comes with the Laravel 5.1. I have create a php file under the tests folder with the name 'UserTest.php'. The content of the file is as follows

<?php

use Illuminate\Foundation\Testing\WithoutMiddleware;
use Illuminate\Foundation\Testing\DatabaseMigrations;
use Illuminate\Foundation\Testing\DatabaseTransactions;

class UserTest extends TestCase
{
    /**
     * A basic test example.
     *
     * @return void
     */



        public function testRegistration()
    {
         echo $this->post('/user/register', ['password' => 'mypass',
                                        'name' => 'Steve Robinson',
                                        'email' => 'stevey@gmail.com']);
             /*->seeJson([
                 'success' => true,
             ]);*/


    }

In the server side I have the following code:

    public function store()
    {
        $credentials = Input::only('name','email', 'password');

   try {
       $user = User::create($credentials);
   } catch (Exception $e) {
       return Response::json(['error' => 'User already exists.'], HttpResponse::HTTP_CONFLICT);
   }

   $token = JWTAuth::fromUser($user);

   return Response::json(compact('token'));
    }

Whenever I run the command 'phpunit' . It throws an error saying object of class UserTest cannot be converted into string. Please tell me what am I doing wrong here.

via Chebli Mohamed