add failing test

plugins/jvm-example/src/test/java/org/elasticsearch/plugin/example/ExampleExternalIT.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.plugin.example;
+
+import org.elasticsearch.test.ESTestCase;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.net.Socket;
+import java.nio.charset.StandardCharsets;
+import java.util.Objects;
+
+public class ExampleExternalIT extends ESTestCase {
+    public void testExample() throws Exception {
+        String host = Objects.requireNonNull(System.getProperty("external.host"));
+        int port = Integer.parseInt(System.getProperty("external.port"));
+        try (Socket socket = new Socket(host, port);
+             BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8))) {
+           assertEquals("TEST", reader.readLine());
+        }
+    }
+}