HADOOP-17947. Provide alternative to Guava VisibleForTesting (#3505)

Reviewed-by: Steve Loughran <stevel@apache.org>
Signed-off-by: Takanobu Asanuma <tasanuma@apache.org>

hadoop-common-project/hadoop-annotations/src/main/java/org/apache/hadoop/classification/VisibleForTesting.java

@@ -0,0 +1,43 @@
+/*
+ * 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.hadoop.classification;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Annotates a program element that exists, or is more widely visible than
+ * otherwise necessary, specifically for use in test code.
+ * More precisely <i>test code within the hadoop-* modules</i>.
+ * Moreover, this gives the implicit scope and stability of:
+ * <pre>
+ *   {@link InterfaceAudience.Private}
+ *   {@link InterfaceStability.Unstable}
+ * </pre>
+ * If external modules need to access/override these methods, then
+ * they MUST be re-scoped as public/limited private.
+ */
+@Retention(RetentionPolicy.CLASS)
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@Documented
+public @interface VisibleForTesting {
+}