title: PHPUnit class TestCase not found
body: <p>I am working on creating a PHP library and want to start writing tests. I am getting an error <code>Fatal error: Class 'PHPUnit\Framework\TestCase' not found</code>. </p>
  
  <p>My project structure is: in my main directory I have composer.json, a src/ directory with all my classes, a tests/ directory with unit/ and acceptance/ subdirectories. The tests I am trying to run are in the the unit/ directory. I am using the command line interface to run the test so the error happens when running <code>phpunit tests/unit/testMyClass.php</code> </p>
  
  <p>testMyClass.php looks like:</p>
  
  <pre><code>&lt;?php
  require 'vendor/autoload.php';
  use PHPUnit\Framework\TestCase;
  
  class MyClassTest extends TestCase {
      public function testCreateMyClass() {
          // Tests are written here
      }
  }
  ?&gt;
  </code></pre>
  
  <p>My composer.json is:  </p>
  
  <pre><code>{
      "require-dev": {
          "phpunit/phpunit": "4.8.*"
      }
      "autoload": {
          "classmap": [
              "src/"
          }
      }
  }
  </code></pre>