title: How can I mock bean returning its own parameter?
body: <p>I have a repository class something like ...</p>
  
  <pre><code>public class StuffRepository {
      public Stuff save(Stuff v);
  }
  </code></pre>
  
  <p>I want to make a mock with @MockBean returning first parameter v.
  How can I do that?</p>
  
  <pre><code>@MockBean
  private StuffRepository stuffRepository;
  
  public void test() {
      given(stuffRepository.save(??)).willReturn(??);
  }
  </code></pre>