title: gmock setting default actions / ON_CALL vs. EXPECT_CALL
body: <p>I don't understand the difference between ON_CALL and EXPECT_CALL when using it to
  specify the default action.</p>
  
  <p>So far I noticed/learned there are two ways to adjust the default action of a mock:</p>
  
  <pre><code>ON_CALL(mock, methodX(_)).WillByDefault(Return(0x01));
  </code></pre>
  
  <p>or</p>
  
  <pre><code>EXPECT_CALL(mock, methodX(_)).WillRepeatedly(Return(0x01));
  </code></pre>
  
  <p>Could someone explain to me:</p>
  
  <ul>
  <li>The difference between the two methods </li>
  <li>The ups and downs of each one</li>
  <li>When is it appropriate to use them (what kind of setup ...)</li>
  </ul>