Getting ErrorException: Array to string conversion when trying to run a phpunit test on laravel controller.

I am trying to run a phpunit test on one of my controllers. I am using a function provided by the laravel frame work called action() and am consistently getting a 1) ListTest::testCreateList ErrorException: Array to string conversion. I have been stuck on this for hours and have NO idea why this would be happening.

1) ListTest::testCreateList ErrorException: Array to string conversion

ConsoleOutput

/Users/jacobshafi/Desktop/Code/api/vendor/laravel/framework/src/Illuminate/Support/helpers.php:686
/Users/jacobshafi/Desktop/Code/api/bootstrap/compiled.php:3976
/Users/jacobshafi/Desktop/Code/api/bootstrap/compiled.php:3966
/Users/jacobshafi/Desktop/Code/api/bootstrap/compiled.php:3959
/Users/jacobshafi/Desktop/Code/api/bootstrap/compiled.php:4043
/Users/jacobshafi/Desktop/Code/api/vendor/laravel/framework/src/Illuminate/Foundation/Testing/ApplicationTrait.php:90
/Users/jacobshafi/Desktop/Code/api/app/tests/ListControllerTest.php:58

ApplicationTrait.php (the action method that is being called in the controller)

public function action($method, $action, $wildcards = array(), $parameters = array(), $files = array(), $server = array(), $content = null, $changeHistory = true)
    {
        $uri = $this->app['url']->action($action, $wildcards, true);

        return $this->call($method, $uri, $parameters, $files, $server, $content, $changeHistory);
    }

ListController.php

class ListController extends BaseController
{
    public function postCreate()
    {
       some code...
    }

ListControllerTest.php

class ListTest extends TestCase {
    public function testCreateList()
    {
        $response = $this->action(
            'POST',
            'App\Controllers\v2\ListController@postCreate',  
            [
                'body' => array(
                    "name" => "open,shared",
                    "users" => array(array("user_id" => $user_id)),
                    "visibility" => "2",
                    "joinability" => "2",
                    "adminship" => "1",
                    "color" => "#2bc069"
                ),
                'headers' => array('Auth' => getTestAuthSender())
            ]
        );
 }

via Chebli Mohamed