title: PowerMock - Singleton Instance test
body: <pre><code>public Data extraMethod(Data data) // interface Data
  {
      Data d = Singleton.getInstance().sort(data.get() , "desc");
      //do something, logical
      return d;
  }
  </code></pre>
  
  <p>How can I mock the object Data(the singleton extra return result), class <code>Singleton</code> has a static method <code>getInstance</code> and no public constructor. I want to test the logical part, test <code>extraMethod</code> without Data sort operation.</p>