Integration of TOS: Add lazy reload interface to common. test

hadoop-cloud-storage-project/hadoop-tos/src/test/java/org/apache/hadoop/fs/tosfs/util/TestLazyReload.java

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+/*
+ * 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.fs.tosfs.util;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Iterator;
+
+public class TestLazyReload {
+  @Test
+  public void testLoadWithFilterCondition() {
+    LazyReload<Integer> integers = new LazyReload<>(() -> {
+      Iterator<Integer> source = Arrays.asList(1, 3, 5, 2, 4, 6).iterator();
+      return buf -> {
+        if (!source.hasNext()) {
+          return true;
+        }
+
+        int pollCnt = 2;
+        while (source.hasNext() && pollCnt-- > 0) {
+          Integer item = source.next();
+          if (item % 2 == 0) {
+            buf.add(item);
+          }
+        }
+
+        return !source.hasNext();
+      };
+    });
+
+    Iterator<Integer> iterator = integers.iterator();
+    Assert.assertTrue(iterator.hasNext());
+    Assert.assertEquals(2, (int) iterator.next());
+    Assert.assertEquals(4, (int) iterator.next());
+    Assert.assertEquals(6, (int) iterator.next());
+    Assert.assertFalse(iterator.hasNext());
+  }
+
+  @Test
+  public void testLoadResultIsIdempotent() {
+    LazyReload<Integer> integers = new LazyReload<>(() -> {
+      Iterator<Integer> source = Arrays.asList(1, 3, 5, 2, 4, 6).iterator();
+      return buf -> {
+        if (!source.hasNext()) {
+          return true;
+        }
+
+        int pollCnt = 2;
+        while (source.hasNext() && pollCnt-- > 0) {
+          Integer item = source.next();
+          buf.add(item);
+        }
+
+        return !source.hasNext();
+      };
+    });
+    Iterator<Integer> iterator1 = integers.iterator();
+    Iterator<Integer> iterator2 = integers.iterator();
+
+    Assert.assertEquals(1, (int) iterator1.next());
+    Assert.assertEquals(1, (int) iterator2.next());
+    Assert.assertEquals(3, (int) iterator1.next());
+    Assert.assertEquals(3, (int) iterator2.next());
+    Assert.assertEquals(5, (int) iterator1.next());
+    Assert.assertEquals(5, (int) iterator2.next());
+
+    Assert.assertEquals(2, (int) iterator1.next());
+    Assert.assertEquals(4, (int) iterator1.next());
+    Assert.assertEquals(6, (int) iterator1.next());
+    Assert.assertEquals(2, (int) iterator2.next());
+    Assert.assertEquals(4, (int) iterator2.next());
+    Assert.assertEquals(6, (int) iterator2.next());
+  }
+}
+