title: What is the purpose of @Rule in Android Espresso UI Test?
body: <p>New to Android Unit Testing with Espresso, under @Rule, what is the purpose of creating a member variable? Does the name of the variable matter? I get the inkling that I need to tell the test unit which activity (or service, class) I'm testing, but is the variable and its scope used anywhere I need to care about?</p>
  
  <pre><code>    @Rule
      public ActivityTestRule&lt;MenuActivity&gt; mActivityTestRule = new ActivityTestRule&lt;&gt;(MenuActivity.class);
  </code></pre>