How to write a test for Elasticsearch custom plugin?

To write tests for you plugin you can use Elasticsearch Cluster Runner. For reference check how MinHash Plugin wrote test.

UPDATE:

I've changed CustomParserPluginTest class to use Elasticsearch Cluster Runner:

import static org.codelibs.elasticsearch.runner.ElasticsearchClusterRunner.newConfigs;import java.util.Map;import junit.framework.TestCase;import org.codelibs.elasticsearch.runner.ElasticsearchClusterRunner;import org.elasticsearch.action.get.GetResponse;import org.elasticsearch.action.index.IndexResponse;import org.elasticsearch.client.Client;import org.elasticsearch.common.bytes.BytesArray;import org.elasticsearch.common.settings.ImmutableSettings;import org.elasticsearch.common.settings.ImmutableSettings.Builder;import org.elasticsearch.common.xcontent.XContentBuilder;import org.elasticsearch.common.xcontent.XContentFactory;import org.elasticsearch.index.get.GetField;import org.junit.Assert;import org.elasticsearch.action.search.SearchResponse;import static org.hamcrest.core.Is.is;public class CustomParserPluginTest extends TestCase {    private ElasticsearchClusterRunner runner;    @Override    protected void setUp() throws Exception {        // create runner instance        runner = new ElasticsearchClusterRunner();        // create ES nodes        runner.onBuild(new ElasticsearchClusterRunner.Builder() {            @Override            public void build(final int number, final Builder settingsBuilder) {            }        }).build(newConfigs().ramIndexStore().numOfNode(1));        // wait for yellow status        runner.ensureYellow();    }    @Override    protected void tearDown() throws Exception {        // close runner        runner.close();        // delete all files        runner.clean();    }    public void test_jsonParsing() throws Exception {        final String index = "test_index";        runner.createIndex(index, ImmutableSettings.builder().build());        runner.ensureYellow(index);        final SearchResponse test = runner.client().prepareSearch(index).setSource(addQuery()).execute().actionGet();    }    private String addQuery() {        return "{\"match_all\":{\"boost\":1.2}}";    }}

I've created es-plugin.properties(pluginrootdirectory\src\main\resources) file with following content which will force elasticsearch instance to load plugin:

plugin=CustomQueryParserPlugin

When you will run the this test you will see in the output that the newly created insance of elasticsearch loaded the plugin.

[2015-04-29 19:22:10,783][INFO ][org.elasticsearch.node ] [Node 1] version[1.5 .0], pid[34360], build[5448160/2015-03-23T14:30:58Z] [2015-04-29 19:22:10,784][INFO ][org.elasticsearch.node ] [Node 1] initializin g ... [2015-04-29 19:22:10,795][INFO ][org.elasticsearch.plugins] [Node 1] loaded [custom_query], sites [] [2015-04-29 19:22:13,342][INFO ][org.elasticsearch.node ] [Node 1] initialized

[2015-04-29 19:22:13,342][INFO ][org.elasticsearch.node ] [Node 1] starting .. .

Hope this helps.