Fatal error: Class 'PHPUnit_Extensions_Selenium2TestCase' not found in *.php - selenium

Question

I am completely new to Seleniu, and am trying to set up PHPUnit with Selenium 2, following this tutorial https://www.youtube.com/watch?v=zva_GETXimI
So far this is what I've done:
Installed PHPUnit using PHAR as instructed here https://phpunit.de/manual/current/en/installation.html
Installed Selenium Server
Upgraded to PHP5.6 (but my Apache is still 2.22 instead of 2.4)
Installed PHPUnit_selenium package using Composer
Created a testLogin.php file:
<?php
class testLogin extends PHPUnit_Extensions_Selenium2TestCase{
public function setUp()
{
$this->setHost('localhost');
$this->setPort(4444);
$this->setBrowser('firefox');
$this->setBrowserUrl('http://localhost/Achievers');
}
}
When I run testLogin.php using 'phpunit testLogin.php' I get an error:
Class 'PHPUnit_Extensions_Selenium2TestCase' not found in /home/osadmin/projects/Sel/testLogin.php on line 5
Since I am just starting out, I have no idea how to fix this. On googling the error, it shows to add this line to my php file:
require_once('PHPUnit/Extensions/Selenium2TestCase.php');
But I'm not sure how I can use this since there is no PHPUnit folder, just a file linked to the PHAR.
Could someone please shed some light on how to fix this issue?
Thanks.
EDIT:
As per Ushakov's suggestion, I tried /path/to/phpunit.phar testLogin.php
But it gives the same error.
If I add this line to the testLogin.php: require_once('/usr/local/bin/phpunit');
and run /path/to/phpunit.phar testLogin.php
I get this:
#!/usr/bin/env php
PHP Notice: Constant __PHPUNIT_PHAR__ already defined in /usr/local/bin/phpunit on line 18
PHP Notice: Constant __PHPUNIT_PHAR_ROOT__ already defined in /usr/local/bin/phpunit on line 19
PHP Fatal error: Cannot redeclare class DeepCopy\DeepCopy in phar:///usr/local/bin/phpunit/myclabs-deep-copy/DeepCopy/DeepCopy.php on line 15

Answer 1

Solved it by adding this line to the PHP file:
require_once 'vendor/autoload.php';
No tutorial I have seen mentions this, but it can be found in github projects

Answer 2

For anyone else coming late to the party - this worked for me:
class testLogin extends \PHPUnit\Extensions\Selenium2TestCase
(Using PHP 7.0.3 and installing Selenium package with Composer ).