<?php

class EchoTest extends TestCase
{
    public function testEcho()
    {
        $this->json('POST', '/echo', ['string' => "first"]);
        $this->json('POST', '/echo', ['string' => "second"]);
        $this->json('POST', '/echo', ['string' => "third"]);
    }
}

<?php

namespace AppHttpControllers;

use AppHttpControllersController;
use IlluminateSupportFacadesInput;

class EchoController extends Controller
{
    public function _echo()
    {
        $input = Input::json()->all();
        var_dump($input['string']);
    }
}

<?php

$app->post('echo', ['uses' => 'EchoController@_echo']);

.string(5) "first"
string(5) "first"
string(5) "first"