add test; fb

sql/src/main/java/org/apache/druid/sql/calcite/run/DruidHook.java

@@ -21,6 +21,8 @@ package org.apache.druid.sql.calcite.run;
 
 import com.google.errorprone.annotations.Immutable;
 import org.apache.calcite.rel.RelNode;
+import org.apache.druid.annotations.SuppressFBWarnings;
+
 import java.io.Closeable;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -74,6 +76,7 @@ public interface DruidHook<T>
 
   void invoke(HookKey<T> key, T object);
 
+  @SuppressFBWarnings({"MS_OOI_PKGPROTECT"})
   Map<HookKey<?>, List<DruidHook<?>>> GLOBAL = new HashMap<>();
 
   static void register(HookKey<?> label, DruidHook<?> hook)

sql/src/test/java/org/apache/druid/sql/calcite/run/DruidHookTest.java

@@ -0,0 +1,35 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.druid.sql.calcite.run;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.junit.Test;
+
+public class DruidHookTest
+{
+  @Test
+  public void testHookKeyEquals()
+  {
+    EqualsVerifier.forClass(DruidHook.HookKey.class)
+        .withNonnullFields("label", "type")
+        .usingGetClass()
+        .verify();
+  }
+}