[TEST] Add test for elastic#14232

Test that ClassSet bindings bound as eager singletons

core/src/test/java/org/elasticsearch/common/util/ExtensionPointTests.java

@@ -0,0 +1,63 @@
+/*
+ * 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.common.util;
+
+import org.elasticsearch.cluster.routing.allocation.decider.AllocationDecider;
+import org.elasticsearch.cluster.routing.allocation.decider.AllocationDeciders;
+import org.elasticsearch.common.inject.*;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ESTestCase;
+
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class ExtensionPointTests extends ESTestCase {
+
+    public void testClassSet() {
+        final ExtensionPoint.ClassSet<AllocationDecider> allocationDeciders = new ExtensionPoint.ClassSet<>("allocation_decider", AllocationDecider.class, AllocationDeciders.class);
+        allocationDeciders.registerExtension(TestAllocationDecider.class);
+        Injector injector = new ModulesBuilder().add(new Module() {
+            @Override
+            public void configure(Binder binder) {
+                binder.bind(Settings.class).toInstance(Settings.EMPTY);
+                binder.bind(Consumer.class).asEagerSingleton();
+                allocationDeciders.bind(binder);
+            }
+        }).createInjector();
+        assertEquals(1, TestAllocationDecider.instances.get());
+
+    }
+
+    public static class Consumer {
+        @Inject
+        public Consumer(Set<AllocationDecider> deciders, TestAllocationDecider other) {
+            // we require the TestAllocationDecider more than once to ensure it's bound as a singleton
+        }
+    }
+
+    public static class TestAllocationDecider extends AllocationDecider {
+        static final AtomicInteger instances = new AtomicInteger(0);
+
+        @Inject
+        public TestAllocationDecider(Settings settings) {
+            super(settings);
+            instances.incrementAndGet();
+        }
+    }
+}