title: Can phpunit use multiple data provider
body: <p>One question in short: can phpunit use multiple data provider when running test?</p>
  
  <p>For example, I have a method called getById, and I need to run both successful and unsuccessful testcases for it.</p>
  
  <p>The successful testcases means that it can return a corresponding record. And for the unsuccessful, the input can fall in two categories: invalid and failed.</p>
  
  <p>The invalid means that the input is not legal, while failed means the input could be valid, but there is no corresponding record with that ID. </p>
  
  <p>So the code goes like this:</p>
  
  <pre><code>/** 
   * @dataProvider provideInvalidId
   * @dataProvider provideFailedId
   */
  public function testGetByIdUnsuccess($id)
  {   
      $this-&gt;assertNull($this-&gt;model-&gt;getById($id));
  }   
  </code></pre>
  
  <p>But it turned out that only the first data provider has been used, ignoring the second one. Though I am not sure this senario is common or not, but here is the question. Can we use multiple data provider? And if we can, how?</p>
  
  <p>PS: did not find too much help in <a href="http://www.phpunit.de/manual/current/en/writing-tests-for-phpunit.html#writing-tests-for-phpunit.data-providers">here</a></p>