Migrate discovery-ec2 YAML tests to Java REST tests (elastic#118427)

Really just to create a starting point for a more comprehensive Java
REST test suite, the test itself is not very interesting.

plugins/discovery-ec2/build.gradle

@@ -6,8 +6,8 @@
  * your election, the "Elastic License 2.0", the "GNU Affero General Public
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
-apply plugin: 'elasticsearch.legacy-yaml-rest-test'
 apply plugin: 'elasticsearch.internal-cluster-test'
+apply plugin: 'elasticsearch.internal-java-rest-test'
 
 esplugin {
   description 'The EC2 discovery plugin allows to use AWS API for the unicast discovery mechanism.'
@@ -29,12 +29,6 @@ dependencies {
   api "joda-time:joda-time:2.10.10"
 }
 
-restResources {
-  restApi {
-    include '_common', 'cluster', 'nodes'
-  }
-}
-
 tasks.named("dependencyLicenses").configure {
   mapping from: /aws-java-sdk-.*/, to: 'aws-java-sdk'
   mapping from: /jackson-.*/, to: 'jackson'

plugins/discovery-ec2/src/javaRestTest/java/org/elasticsearch/discovery/ec2/DiscoveryEc2PluginLoadedIT.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.discovery.ec2;
+
+import org.elasticsearch.client.Request;
+import org.elasticsearch.test.cluster.ElasticsearchCluster;
+import org.elasticsearch.test.rest.ESRestTestCase;
+import org.junit.ClassRule;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Objects;
+
+import static org.hamcrest.Matchers.hasItem;
+
+public class DiscoveryEc2PluginLoadedIT extends ESRestTestCase {
+
+    @ClassRule
+    public static ElasticsearchCluster cluster = ElasticsearchCluster.local().plugin("discovery-ec2").build();
+
+    @Override
+    protected String getTestRestCluster() {
+        return cluster.getHttpAddresses();
+    }
+
+    public void testPluginLoaded() throws IOException {
+        final var nodesInfoResponse = assertOKAndCreateObjectPath(client().performRequest(new Request("GET", "/_nodes/plugins")));
+        for (final var nodeId : nodesInfoResponse.evaluateMapKeys("nodes")) {
+            final var pluginCount = asInstanceOf(List.class, nodesInfoResponse.evaluateExact("nodes", nodeId, "plugins")).size();
+            final var pluginNames = new HashSet<String>();
+            for (int i = 0; i < pluginCount; i++) {
+                pluginNames.add(
+                    Objects.requireNonNull(nodesInfoResponse.evaluateExact("nodes", nodeId, "plugins", Integer.toString(i), "name"))
+                );
+            }
+            assertThat(pluginNames, hasItem("discovery-ec2"));
+        }
+    }
+
+}

test/framework/src/main/java/org/elasticsearch/test/rest/ObjectPath.java

@@ -70,11 +70,24 @@ public <T> T evaluate(String path) throws IOException {
     /**
      * Returns the object corresponding to the provided path if present, null otherwise
      */
-    @SuppressWarnings("unchecked")
     public <T> T evaluate(String path, Stash stash) throws IOException {
-        String[] parts = parsePath(path);
+        return evaluateExact(stash, parsePath(path));
+    }
+
+    /**
+     * Returns the object corresponding to the provided path if present, null otherwise
+     */
+    public <T> T evaluateExact(String... path) throws IOException {
+        return evaluateExact(Stash.EMPTY, path);
+    }
+
+    /**
+     * Returns the object corresponding to the provided path if present, null otherwise
+     */
+    @SuppressWarnings("unchecked")
+    public <T> T evaluateExact(Stash stash, String... path) throws IOException {
         Object result = this.object;
-        for (String part : parts) {
+        for (String part : path) {
             result = evaluate(part, result, stash);
             if (result == null) {
                 return null;