Symfony unit testing - php

Question

Following is my directory structure:
|-vendor
|---bin
|---phpunit
|---autoload.php
|---psr
|---sebastian
|---phar-io
|---composer
|---symfony
|-.htaccess
|-composer.lock
|-includes
|---application_top.php
|-routes
|---routes.php
|-modules
|---Controllers
|----CheckoutGatewayController.php
|-tests
|---Controllers
|----tests_common_includes.php
|-composer.phar
I am trying to run ./vendor/bin/simple-phpunit --bootstrap tests/tests_common_includes.php tests/Controllers/CheckoutGatewayTests.php from my base directory but it gives me error Class 'tests/Controllers/CheckoutGatewayTests' could not be found in 'tests/Controllers/CheckoutGatewayTests.php'.
If I try ./vendor/bin/phpunit --bootstrap tests/tests_common_includes.php tests/Controllers/CheckoutGatewayTests.php then I get the error Unable to guess the Kernel directory. I tried to look up symfony's documentation : it suggests using either -c app option or changing phpunit.dist.xml file. But I have neither of those in my directory. There is no xml file and no app folder.
How can I execute my tests? My test file CheckoutGatewayTests.php looks like this :
<?php
use \Controllers\CheckoutGatewayController;
use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
class CheckoutGatewayTests extends WebTestCase {
public function testChargebackCallback() {
$client = static::createClient();
$client->request('GET', '/post/hello-world');
}
}
Edit: my composer.json file
{
"require": {
"guzzlehttp/guzzle": "~6.0",
"psr/log": "^1.0",
"zircote/swagger-php": "^2.0",
"sentry/sentry": "^1.8",
"aws/aws-sdk-php": "^3.52",
"league/flysystem-aws-s3-v3": "~1.0",
"symfony/routing": "^3.4",
"symfony/http-kernel": "^3.4",
"symfony/dependency-injection": "^3.4",
"symfony/framework-bundle": "^3.4",
"prbdias/mbway-php": "0.1"
},
"require-dev": {
"phpunit/phpunit": "^6"
},
"config": {
"optimize-autoloader": true
},
"autoload": {
"psr-4": {
"": ["modules/", "tests/","routes/"]
}
}
}