code: @Test public void testGetClusters() throws AmbariException {
    clusters.addCluster("c1");
    Cluster c1=clusters.getCluster("c1");
    c1.setDesiredStackVersion(new StackId("HDP-0.1"));
    ClusterRequest r=new ClusterRequest(null,null,null,null);
    Set<ClusterResponse> resp=controller.getClusters(Collections.singleton(r));
    Assert.assertEquals(1,resp.size());
    ClusterResponse resp1=resp.iterator().next();
    Assert.assertEquals(c1.getClusterId(),resp1.getClusterId().longValue());
    Assert.assertEquals(c1.getClusterName(),resp1.getClusterName());
    Assert.assertEquals(c1.getDesiredStackVersion().getStackId(),resp1.getDesiredStackVersion());
  }
  