Q: Testing a Solr distributed component I have developed a custom Solr search component for which I need to write unit tests. As I have seen in the code of other Solr components, writing unit tests in Solr is done by extending the SolrTestCaseJ4 class. Unfortunately, SolrTestCaseJ4 doesn't deal with testing in a distributed setting, and my custom component works only in such a setting. As a matter of fact, my component deliberately returns empty responses when not in a distributed setting.
I'm trying to think of a way to use the BaseDistributedSearchTestCase class to test my component. The problem with BaseDistributedSearchTestCase is that how it works won't solve my issue. When using BaseDistributedSearchTestCase you define a single test method where you index all the documents and perform some queries. Running the tests executes the requests both on a distributed setting and on a single core setting. It then compares the responses of each setting to verify their equality. I cannot explicitly assert anything in that flow.
How do I write unit tests for a Solr distributed component?

A: In Solr 4.7 has been added a class, MiniSolrCloudCluster, that actually "deploys" locally (and if you want ram only or on a temp dir) a complete solr cluster, with zookeeper, shards and everything, for your tests.
You can find the jira here : https://issues.apache.org/jira/browse/SOLR-5865
I've successfully used it to perform tests on solr distributed components, taking example from Solr tests, as follows :

    private static MiniSolrCloudCluster miniCluster;
    private static CloudSolrServer cloudSolrServer;

    @BeforeClass
    public static void setup() throws Exception {
        miniCluster = new MiniSolrCloudCluster(2, null, new File("src/main/solr/solr.xml"), null, null);
        uploadConfigToZk("src/main/solr/content/conf/", "content");

        // override settings in the solrconfig include
        System.setProperty("solr.tests.maxBufferedDocs", "100000");
        System.setProperty("solr.tests.maxIndexingThreads", "-1");
        System.setProperty("solr.tests.ramBufferSizeMB", "100");
        // use non-test classes so RandomizedRunner isn't necessary
        System.setProperty("solr.tests.mergeScheduler", "org.apache.lucene.index.ConcurrentMergeScheduler");
        System.setProperty("solr.directoryFactory", "solr.RAMDirectoryFactory");        

        cloudSolrServer = new CloudSolrServer(miniCluster.getZkServer().getZkAddress(), false);
        cloudSolrServer.setRequestWriter(new RequestWriter());
        cloudSolrServer.setParser(new XMLResponseParser());
        cloudSolrServer.setDefaultCollection("content");
        cloudSolrServer.setParallelUpdates(false);
        cloudSolrServer.connect();

        createCollection(cloudSolrServer, "content", 2, 1, "content");

    }

    protected static void uploadConfigToZk(String configDir, String configName) throws Exception {
        SolrZkClient zkClient = null;
        try {
            zkClient = new SolrZkClient(miniCluster.getZkServer().getZkAddress(), 10000, 45000, null);
            uploadConfigFileToZk(zkClient, configName, "solrconfig.xml", new File(configDir, "solrconfig.xml"));
            uploadConfigFileToZk(zkClient, configName, "schema.xml", new File(configDir, "schema.xml"));
            uploadConfigFileToZk(zkClient, configName, "stopwords_en.txt", new File(configDir, "stopwords_en.txt"));
            uploadConfigFileToZk(zkClient, configName, "stopwords_it.txt", new File(configDir, "stopwords_it.txt"));

            System.out.println(zkClient.getChildren(ZkController.CONFIGS_ZKNODE + "/" + configName, null, true));
        } finally {
            if (zkClient != null)
                zkClient.close();
        }
    }

    protected static void uploadConfigFileToZk(SolrZkClient zkClient, String configName, String nameInZk, File file) throws Exception {
        zkClient.makePath(ZkController.CONFIGS_ZKNODE + "/" + configName + "/" + nameInZk, file, false, true);
    }

    @AfterClass
    public static void shutDown() throws Exception {
        miniCluster.shutdown();
    }

    protected static NamedList createCollection(CloudSolrServer server, String name, int numShards, int replicationFactor, String configName) throws Exception {
        ModifiableSolrParams modParams = new ModifiableSolrParams();
        modParams.set(CoreAdminParams.ACTION, CollectionAction.CREATE.name());
        modParams.set("name", name);
        modParams.set("numShards", numShards);
        modParams.set("replicationFactor", replicationFactor);
        modParams.set("collection.configName", configName);
        QueryRequest request = new QueryRequest(modParams);
        request.setPath("/admin/collections");
        return server.request(request);
    }

    @Test
    public void test() throws Exception {
      // Do you stuff here using cloudSolrServer as a normal solrServer
    }


