title: PHPUnit load test suite with recursive directory expression
body: <p>I am trying to define my <code>phpunit.xml</code> configuration with a custom test suite, which loads all Unit tests in desired folder recursively.</p>
  
  <p>Folder path examples:</p>
  
  <pre><code>tests/path/Unit/MyTest.php
  tests/path/path/Unit/MyTest.php
  tests/path/path/path/Unit/MyTest.php
  tests/path/path/path/path/Unit/MyTest.php
  ...
  tests/{.../}/Unit/MyTest.php
  </code></pre>
  
  <p>I can define my suite like this:</p>
  
  <pre><code>&lt;testsuites&gt;
      &lt;testsuite name="Project Unit Test Suite"&gt;
          &lt;directory&gt;tests/*/Unit&lt;/directory&gt;
          &lt;directory&gt;tests/*/*/Unit&lt;/directory&gt;
          &lt;directory&gt;tests/*/*/*/Unit&lt;/directory&gt;
          &lt;directory&gt;tests/*/*/*/*/Unit&lt;/directory&gt;
          ...
      &lt;/testsuite&gt;
  &lt;/testsuites&gt;
  </code></pre>
  
  <p>Is there a way to iterate over all sub-folders that my expression would be only a single line?</p>