backupscript/tests/CommandBackupTest.php

<?php 
namespace App\Tests;

use PHPUnit\Framework\TestCase;
use Symfony\Component\Console\Application;
use Symfony\Component\Console\Tester\CommandTester;
use App\CommandBackup;

class CommandBackupTest extends \PHPUnit\Framework\TestCase
{
    public function testInvalidConfig()
    {

        $applicationd = new Application('backup', "1.1.1");

        $applicationd->add(new CommandBackup());


        $command = $applicationd->find('backup');
        $commandTester = new CommandTester($command);
        $commandTester->execute(['config'=>"empty"]);

        $output = $commandTester->getDisplay();
        $this->assertStringContainsString('backup', $output);
    }
}