Bug/feature/missingdocumentation: How to include phpunit tokens?

[artfulrobot]

Describe the bug

While working on phpunit classes, diagnostics show up lots of missing methods making an error on almost every line. This is because it doesn't know about the phpunit classes.

To Reproduce

e.g. this:

<?php
class ParticipantTest extends \PHPUnit\Framework\TestCase {
  function testSomething() {
    $this->assertTrue(TRUE);
  }
}

Will show an error Undefined type 'PHPUnit\Framework\TestCase'. and Undefined method 'assertTrue'.

Expected behavior

I'd like to be able to say "hey, you should really look in phpunit.phar for extra symbols"

Screenshots

Desktop (please complete the following information):

• OS: Linuxes
• Version 2.2.1