updated libraryTestCase file

libraryTestCase.php

<?php

use Library\App\LibraryRoute;
use Slim\Http\Environment;
use Slim\Http\Request;
use PHPUnit\Framework\TestCase;
class LibraryTestCase extends TestCase
{
    protected $app;
    public function setUp()
    {
        $this->app = (new LibraryRoute())->get();
    }
    public function testLibraryGet() {
        $env = Environment::mock([
            'REQUEST_METHOD' => 'GET',
            'REQUEST_URI'    => '/',
            ]);
        $req = Request::createFromEnvironment($env);
        $this->app->getContainer()['request'] = $req;
        $response = $this->app->run(true); //tells Slim to run the app instance and instead of return HTTP headers and body of the response it should return an object.
        $this->assertSame($response->getStatusCode(), 200);
        $this->assertSame((string)$response->getBody(), "Welcome to the Adroit Library Demo.");
    } 
}