[HUDI-2579] Make deltastreamer checkpoint state merging more explicit (#3820)

Co-authored-by: Sivabalan Narayanan <n.siva.b@gmail.com>

hudi-client/hudi-client-common/src/test/java/org/apache/hudi/utils/TestTransactionUtils.java

@@ -0,0 +1,98 @@
+/*
+ * 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.hudi.utils;
+
+import org.apache.hadoop.fs.Path;
+import org.apache.hudi.client.utils.TransactionUtils;
+import org.apache.hudi.common.model.HoodieCommitMetadata;
+import org.apache.hudi.common.table.HoodieTableMetaClient;
+import org.apache.hudi.common.table.timeline.HoodieActiveTimeline;
+import org.apache.hudi.common.table.timeline.HoodieInstant;
+import org.apache.hudi.common.table.timeline.HoodieTimeline;
+import org.apache.hudi.common.testutils.HoodieCommonTestHarness;
+import org.apache.hudi.common.util.Option;
+import org.apache.hudi.config.HoodieWriteConfig;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+
+public class TestTransactionUtils extends HoodieCommonTestHarness {
+
+  @BeforeEach
+  public void setUp() throws Exception {
+    init();
+  }
+
+  public void init() throws Exception {
+    initPath();
+    initMetaClient();
+    metaClient.getFs().mkdirs(new Path(basePath));
+  }
+
+  @Test
+  public void testCheckpointStateMerge() throws IOException {
+    HoodieActiveTimeline timeline = new HoodieActiveTimeline(metaClient);
+
+    // Create completed commit with deltastreamer checkpoint state
+    HoodieInstant commitInstantWithCheckpointState = new HoodieInstant(
+        true,
+        HoodieTimeline.COMMIT_ACTION,
+        HoodieActiveTimeline.createNewInstantTime()
+    );
+    timeline.createNewInstant(commitInstantWithCheckpointState);
+
+    HoodieCommitMetadata metadataWithCheckpoint = new HoodieCommitMetadata();
+    String checkpointVal = "00001";
+    metadataWithCheckpoint.addMetadata(HoodieWriteConfig.DELTASTREAMER_CHECKPOINT_KEY, checkpointVal);
+    timeline.saveAsComplete(
+        commitInstantWithCheckpointState,
+        Option.of(metadataWithCheckpoint.toJsonString().getBytes(StandardCharsets.UTF_8))
+    );
+
+    // Inflight commit without checkpoint metadata
+    HoodieInstant commitInstantWithoutCheckpointState = new HoodieInstant(
+        true,
+        HoodieTimeline.COMMIT_ACTION,
+        HoodieActiveTimeline.createNewInstantTime()
+    );
+    timeline.createNewInstant(commitInstantWithoutCheckpointState);
+    HoodieCommitMetadata metadataWithoutCheckpoint = new HoodieCommitMetadata();
+
+    // Ensure that checkpoint state is merged in from previous completed commit
+    MockTransactionUtils.assertCheckpointStateWasMerged(metaClient, metadataWithoutCheckpoint, checkpointVal);
+  }
+
+  private static class MockTransactionUtils extends TransactionUtils {
+
+    public static void assertCheckpointStateWasMerged(
+        HoodieTableMetaClient metaClient,
+        HoodieCommitMetadata currentMetadata,
+        String expectedCheckpointState) {
+      TransactionUtils.mergeCheckpointStateFromPreviousCommit(metaClient, Option.of(currentMetadata));
+      assertEquals(
+          expectedCheckpointState,
+          currentMetadata.getExtraMetadata().get(HoodieWriteConfig.DELTASTREAMER_CHECKPOINT_KEY)
+      );
+    }
+  }
+}