title: How does replaceFromWith with in AdviceWithRouteBuilder
body: <p>I'm using AdviceWithRouteBuilder in my unit tests and I'm not sure how the replaceFromWith method works. The routes I'm testing looks something like this:</p>
  
  <pre><code>from(FTP_ENDPOINT)
      choice()
          when(predicateA)
              to("routeA")
          when(predicateB)
              to("routeB)
          otherwise()
              to("routeC");
  
  from("routeA")
      to(SOMEWHERE)
  
  from("routeB")
      to(SOMEWHER)
  
  etc...
  </code></pre>
  
  <p>My unit tests uses an AdviceWithRouteBuilder to replace the FTP_ENDPOINT with "direct:start" like this:</p>
  
  <pre><code>context.getRouteDefinitions().get(0).adviceWith(context, new AdviceWithRouteBuilder() {
      @Override
      public void configure() throws Exception {
          replaceFromWith("direct:start);
      }
  });
  </code></pre>
  
  <p>My question is, how does replaceFromWith know which endpoint to replace? I only want to replace the FTP_ENDPOINT.</p>