[BEAM-222] Respect checkpointing contract in TestCountingSource

sdks/java/core/src/test/java/org/apache/beam/sdk/runners/dataflow/TestCountingSource.java

@@ -155,7 +155,11 @@ public boolean requiresDeduping() {
     return dedup;
   }
 
-  private class CountingSourceReader extends UnboundedReader<KV<Integer, Integer>> {
+  /**
+   * Public only so that the checkpoint can be conveyed from {@link #getCheckpointMark()} to
+   * {@link TestCountingSource#createReader(PipelineOptions, CounterMark)} without cast.
+   */
+  public class CountingSourceReader extends UnboundedReader<KV<Integer, Integer>> {
     private int current;
 
     public CountingSourceReader(int startingPoint) {
@@ -164,21 +168,20 @@ public CountingSourceReader(int startingPoint) {
 
     @Override
     public boolean start() {
-      return true;
+      return advance();
     }
 
     @Override
     public boolean advance() {
-      if (current < numMessagesPerShard - 1) {
-        // If testing dedup, occasionally insert a duplicate value;
-        if (dedup && ThreadLocalRandom.current().nextInt(5) == 0) {
-          return true;
-        }
-        current++;
-        return true;
-      } else {
+      if (current >= numMessagesPerShard) {
         return false;
       }
+      // If testing dedup, occasionally insert a duplicate value;
+      if (current >= 0 && dedup && ThreadLocalRandom.current().nextInt(5) == 0) {
+        return true;
+      }
+      current++;
+      return current < numMessagesPerShard;
     }
 
     @Override
@@ -216,12 +219,14 @@ public Instant getWatermark() {
     }
 
     @Override
-    public CheckpointMark getCheckpointMark() {
+    public CounterMark getCheckpointMark() {
       if (throwOnFirstSnapshot && !thrown) {
         thrown = true;
         LOG.error("Throwing exception while checkpointing counter");
         throw new RuntimeException("failed during checkpoint");
       }
+      // The checkpoint can assume all records read, including the current, have
+      // been commited.
       return new CounterMark(current);
     }
 
@@ -234,7 +239,12 @@ public long getSplitBacklogBytes() {
   @Override
   public CountingSourceReader createReader(
       PipelineOptions options, @Nullable CounterMark checkpointMark) {
-    return new CountingSourceReader(checkpointMark != null ? checkpointMark.current : 0);
+    if (checkpointMark == null) {
+      LOG.debug("creating reader");
+    } else {
+      LOG.debug("restoring reader from checkpoint with current = {}", checkpointMark.current);
+    }
+    return new CountingSourceReader(checkpointMark != null ? checkpointMark.current : -1);
   }
 
   @Override

sdks/java/core/src/test/java/org/apache/beam/sdk/runners/dataflow/TestCountingSourceTest.java

@@ -0,0 +1,56 @@
+/*
+ * 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.beam.sdk.runners.dataflow;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.beam.sdk.options.PipelineOptions;
+import org.apache.beam.sdk.options.PipelineOptionsFactory;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.io.IOException;
+
+/**
+ * Test the TestCountingSource.
+ */
+@RunWith(JUnit4.class)
+public class TestCountingSourceTest {
+  @Test
+  public void testRespectsCheckpointContract() throws IOException {
+    TestCountingSource source = new TestCountingSource(3);
+    PipelineOptions options = PipelineOptionsFactory.create();
+    TestCountingSource.CountingSourceReader reader =
+        source.createReader(options, null /* no checkpoint */);
+    assertTrue(reader.start());
+    assertEquals(0L, (long) reader.getCurrent().getValue());
+    assertTrue(reader.advance());
+    assertEquals(1L, (long) reader.getCurrent().getValue());
+    TestCountingSource.CounterMark checkpoint = reader.getCheckpointMark();
+    checkpoint.finalizeCheckpoint();
+    reader = source.createReader(options, checkpoint);
+    assertTrue(reader.start());
+    assertEquals(2L, (long) reader.getCurrent().getValue());
+    assertFalse(reader.advance());
+  }
+}