title: Run one-time, async callback before all junit tests
body: <p>I would like to call some methods before run all tests.
  Library provides initializer which preparing device to use:</p>
  
  <pre><code>    SomeLibraryInitializer.init(new SomeLibraryInitializer.Callback() {
          @Override
          public void onFinish() {
  
          }
      });
  </code></pre>
  
  <p>The library is ready to use when onFinish is called.</p>
  
  <p>Can't mock library classes (proguard in use), so I have to use that initializer for my <code>JUnit tests</code>. </p>
  
  <p>Is there any way to wait until callback <code>onFinish()</code> is called?</p>
  
  <p>Tried with  <code>ShadowApplication.runBackgroundTasks();</code> and Semaphore, but not seem to work.
  I'm using <code>@BeforeClass</code> Annotation to run it before all tests.</p>