jose-torres commented on code in PR #57495:
URL: https://github.com/apache/spark/pull/57495#discussion_r3648667977


##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2ForeachBatchHandlerSuite.scala:
##########
@@ -0,0 +1,949 @@
+/*
+ * 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.spark.sql.pipelines.autocdc
+
+import org.scalatest.BeforeAndAfter
+
+import org.apache.spark.sql.{functions => F, AnalysisException, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+/**
+ * End-to-end unit tests for [[Scd2ForeachBatchHandler]]. Unlike the focused 
unit suites that
+ * exercise individual [[Scd2BatchProcessor]] stages in isolation, these drive 
the entire
+ * microbatch reconciliation pipeline - validation, preprocessing, 
affected-row pull-in from both
+ * side tables, decomposition, start/end reconciliation, aux routing, and the 
two `MERGE INTO`
+ * writes - through the public `execute` entrypoint against an in-memory v2 
catalog.
+ *
+ * They are the first place the cross-microbatch stateful behaviors 
(out-of-order arrivals, no-op
+ * run coalescing across batches, tombstone-driven suppression, and 
auxiliary-table garbage
+ * collection) can be observed against materialized target and auxiliary 
tables, so the idempotency
+ * / GC / cross-batch scenarios are emphasized here.
+ *
+ * The default flow tracks every persisted user column (`value`) under key 
`id`, sequences by
+ * `seq`, and treats `is_delete = true` rows as deletes.
+ */
+class Scd2ForeachBatchHandlerSuite
+    extends QueryTest
+    with SharedSparkSession
+    with BeforeAndAfter
+    with AutoCdcCatalogExecutionTestBase {
+
+  private val sourceSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add("seq", LongType)
+    .add("is_delete", BooleanType)
+
+  /** The SCD2 cdc-metadata struct carries a single `recordStartAt` field 
(unlike SCD1's two). */
+  private val scd2MetadataSchema: StructType = 
Scd2BatchProcessor.cdcMetadataColSchema(LongType)
+
+  /** Canonical SCD2 row schema: persisted user columns + framework start/end 
+ cdc metadata. */
+  private val canonicalSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add(Scd2BatchProcessor.startAtColName, LongType, nullable = true)
+    .add(Scd2BatchProcessor.endAtColName, LongType, nullable = true)
+    .add(AutoCdcReservedNames.cdcMetadataColName, scd2MetadataSchema, nullable 
= false)
+
+  /** Auxiliary table schema: canonical schema plus the aux-only 
logical-delete marker column. */
+  private val auxSchema = canonicalSchema
+    .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = true)
+
+  /** Target table schema is exactly the canonical schema. */
+  private val targetSchema = canonicalSchema
+
+  private val processor = Scd2BatchProcessor(
+    changeArgs = ChangeArgs(
+      keys = Seq(UnqualifiedColumnName("id")),
+      sequencing = F.col("seq"),
+      storedAsScdType = ScdType.Type2,
+      deleteCondition = Some(F.col("is_delete")),
+      // Persist only id + value; seq / is_delete are control columns and must 
not be stored.

Review Comment:
   nit: "Must" not will be confusing to future readers. Users of the API will 
often want not to store them but we can't safely assume they'll never be stored.



##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2ForeachBatchHandlerSuite.scala:
##########
@@ -0,0 +1,949 @@
+/*
+ * 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.spark.sql.pipelines.autocdc
+
+import org.scalatest.BeforeAndAfter
+
+import org.apache.spark.sql.{functions => F, AnalysisException, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+/**
+ * End-to-end unit tests for [[Scd2ForeachBatchHandler]]. Unlike the focused 
unit suites that
+ * exercise individual [[Scd2BatchProcessor]] stages in isolation, these drive 
the entire
+ * microbatch reconciliation pipeline - validation, preprocessing, 
affected-row pull-in from both
+ * side tables, decomposition, start/end reconciliation, aux routing, and the 
two `MERGE INTO`
+ * writes - through the public `execute` entrypoint against an in-memory v2 
catalog.
+ *
+ * They are the first place the cross-microbatch stateful behaviors 
(out-of-order arrivals, no-op
+ * run coalescing across batches, tombstone-driven suppression, and 
auxiliary-table garbage
+ * collection) can be observed against materialized target and auxiliary 
tables, so the idempotency
+ * / GC / cross-batch scenarios are emphasized here.
+ *
+ * The default flow tracks every persisted user column (`value`) under key 
`id`, sequences by
+ * `seq`, and treats `is_delete = true` rows as deletes.
+ */
+class Scd2ForeachBatchHandlerSuite
+    extends QueryTest
+    with SharedSparkSession
+    with BeforeAndAfter
+    with AutoCdcCatalogExecutionTestBase {
+
+  private val sourceSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add("seq", LongType)
+    .add("is_delete", BooleanType)
+
+  /** The SCD2 cdc-metadata struct carries a single `recordStartAt` field 
(unlike SCD1's two). */
+  private val scd2MetadataSchema: StructType = 
Scd2BatchProcessor.cdcMetadataColSchema(LongType)
+
+  /** Canonical SCD2 row schema: persisted user columns + framework start/end 
+ cdc metadata. */
+  private val canonicalSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add(Scd2BatchProcessor.startAtColName, LongType, nullable = true)
+    .add(Scd2BatchProcessor.endAtColName, LongType, nullable = true)
+    .add(AutoCdcReservedNames.cdcMetadataColName, scd2MetadataSchema, nullable 
= false)
+
+  /** Auxiliary table schema: canonical schema plus the aux-only 
logical-delete marker column. */
+  private val auxSchema = canonicalSchema
+    .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = true)
+
+  /** Target table schema is exactly the canonical schema. */
+  private val targetSchema = canonicalSchema
+
+  private val processor = Scd2BatchProcessor(
+    changeArgs = ChangeArgs(
+      keys = Seq(UnqualifiedColumnName("id")),
+      sequencing = F.col("seq"),
+      storedAsScdType = ScdType.Type2,
+      deleteCondition = Some(F.col("is_delete")),
+      // Persist only id + value; seq / is_delete are control columns and must 
not be stored.
+      columnSelection = Some(
+        ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("seq"), UnqualifiedColumnName("is_delete"))
+        )
+      )
+    ),
+    resolvedSequencingType = LongType
+  )
+
+  private def createAuxTable(seedRows: Row*): Unit =
+    createTable(defaultAuxIdent, defaultAuxTableIdentifier, auxSchema, 
seedRows: _*)
+
+  private def createTargetTable(seedRows: Row*): Unit =
+    createTable(defaultTargetIdent, defaultTargetTableIdentifier, 
targetSchema, seedRows: _*)
+
+  private def auxTable: DataFrame = 
spark.read.table(defaultAuxTableIdentifier.quotedString)
+
+  private def targetTable: DataFrame = 
spark.read.table(defaultTargetTableIdentifier.quotedString)
+
+  private def execWith(p: Scd2BatchProcessor): Scd2ForeachBatchHandler = 
Scd2ForeachBatchHandler(
+    batchProcessor = p,
+    auxiliaryTableIdentifier = defaultAuxTableIdentifier,
+    targetTableIdentifier = defaultTargetTableIdentifier
+  )
+
+  private def exec: Scd2ForeachBatchHandler = execWith(processor)
+
+  /** A source UPSERT event: `(id, value, seq, is_delete = false)`. */
+  private def upsert(id: Int, value: String, seq: Long): Row = Row(id, value, 
seq, false)
+
+  /** A source DELETE event: `(id, null, seq, is_delete = true)`. */
+  private def del(id: Int, seq: Long): Row = Row(id, null, seq, true)
+
+  /** The cdc-metadata struct value for a given `recordStartAt`. */
+  private def meta(recordStartAt: Long): Row = Row(recordStartAt)
+
+  /** A canonical target row `(id, value, startAt, endAt, 
meta(recordStartAt))`. */
+  private def targetRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt))
+
+  /** A canonical aux row `(id, value, startAt, endAt, meta(recordStartAt), 
deletedByBatchId)`. */
+  private def auxRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long,
+      deletedByBatchId: java.lang.Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt), deletedByBatchId)
+
+  /** Run a microbatch of source rows through the default handler. */
+  private def runBatch(batchId: Long)(rows: Row*): Unit =
+    exec.execute(microbatchOf(sourceSchema)(rows: _*), batchId)
+
+  /**
+   * Run `rows` as batch `batchId`, capture both tables, then replay the 
identical batch under the
+   * same `batchId` and assert both tables are byte-for-byte unchanged. Models 
a crash/redelivery
+   * where a committed microbatch is reprocessed.
+   */
+  private def assertReplayStable(batchId: Long)(rows: Row*): Unit = {
+    runBatch(batchId)(rows: _*)
+    val targetAfterFirst = targetTable.collect().toSeq
+    val auxAfterFirst = auxTable.collect().toSeq
+
+    runBatch(batchId)(rows: _*)
+    checkAnswer(targetTable, targetAfterFirst)
+    checkAnswer(auxTable, auxAfterFirst)
+  }
+
+  test("a record with a null sequencing value fails the microbatch without 
applying any changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(1, "bad", null, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 77L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_SEQUENCE",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "77",
+        "nullCount" -> "1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("a record with a null key fails the microbatch without applying any 
changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(null, "bad", 10L, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 7L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_KEY",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "7",
+        "nullKeyCounts" -> "`id`=1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("an empty microbatch leaves both tables unchanged") {

Review Comment:
   We should run this test with target + aux both empty and both non-empty to 
flush out any (current or future) edge cases, since empty batches are something 
we'll have to expect in general.



##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2ForeachBatchHandlerSuite.scala:
##########
@@ -0,0 +1,949 @@
+/*
+ * 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.spark.sql.pipelines.autocdc
+
+import org.scalatest.BeforeAndAfter
+
+import org.apache.spark.sql.{functions => F, AnalysisException, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+/**
+ * End-to-end unit tests for [[Scd2ForeachBatchHandler]]. Unlike the focused 
unit suites that
+ * exercise individual [[Scd2BatchProcessor]] stages in isolation, these drive 
the entire
+ * microbatch reconciliation pipeline - validation, preprocessing, 
affected-row pull-in from both
+ * side tables, decomposition, start/end reconciliation, aux routing, and the 
two `MERGE INTO`
+ * writes - through the public `execute` entrypoint against an in-memory v2 
catalog.
+ *
+ * They are the first place the cross-microbatch stateful behaviors 
(out-of-order arrivals, no-op
+ * run coalescing across batches, tombstone-driven suppression, and 
auxiliary-table garbage
+ * collection) can be observed against materialized target and auxiliary 
tables, so the idempotency
+ * / GC / cross-batch scenarios are emphasized here.
+ *
+ * The default flow tracks every persisted user column (`value`) under key 
`id`, sequences by
+ * `seq`, and treats `is_delete = true` rows as deletes.
+ */
+class Scd2ForeachBatchHandlerSuite
+    extends QueryTest
+    with SharedSparkSession
+    with BeforeAndAfter
+    with AutoCdcCatalogExecutionTestBase {
+
+  private val sourceSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add("seq", LongType)
+    .add("is_delete", BooleanType)
+
+  /** The SCD2 cdc-metadata struct carries a single `recordStartAt` field 
(unlike SCD1's two). */
+  private val scd2MetadataSchema: StructType = 
Scd2BatchProcessor.cdcMetadataColSchema(LongType)
+
+  /** Canonical SCD2 row schema: persisted user columns + framework start/end 
+ cdc metadata. */
+  private val canonicalSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add(Scd2BatchProcessor.startAtColName, LongType, nullable = true)
+    .add(Scd2BatchProcessor.endAtColName, LongType, nullable = true)
+    .add(AutoCdcReservedNames.cdcMetadataColName, scd2MetadataSchema, nullable 
= false)
+
+  /** Auxiliary table schema: canonical schema plus the aux-only 
logical-delete marker column. */
+  private val auxSchema = canonicalSchema
+    .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = true)
+
+  /** Target table schema is exactly the canonical schema. */
+  private val targetSchema = canonicalSchema
+
+  private val processor = Scd2BatchProcessor(
+    changeArgs = ChangeArgs(
+      keys = Seq(UnqualifiedColumnName("id")),
+      sequencing = F.col("seq"),
+      storedAsScdType = ScdType.Type2,
+      deleteCondition = Some(F.col("is_delete")),
+      // Persist only id + value; seq / is_delete are control columns and must 
not be stored.
+      columnSelection = Some(
+        ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("seq"), UnqualifiedColumnName("is_delete"))
+        )
+      )
+    ),
+    resolvedSequencingType = LongType
+  )
+
+  private def createAuxTable(seedRows: Row*): Unit =
+    createTable(defaultAuxIdent, defaultAuxTableIdentifier, auxSchema, 
seedRows: _*)
+
+  private def createTargetTable(seedRows: Row*): Unit =
+    createTable(defaultTargetIdent, defaultTargetTableIdentifier, 
targetSchema, seedRows: _*)
+
+  private def auxTable: DataFrame = 
spark.read.table(defaultAuxTableIdentifier.quotedString)
+
+  private def targetTable: DataFrame = 
spark.read.table(defaultTargetTableIdentifier.quotedString)
+
+  private def execWith(p: Scd2BatchProcessor): Scd2ForeachBatchHandler = 
Scd2ForeachBatchHandler(
+    batchProcessor = p,
+    auxiliaryTableIdentifier = defaultAuxTableIdentifier,
+    targetTableIdentifier = defaultTargetTableIdentifier
+  )
+
+  private def exec: Scd2ForeachBatchHandler = execWith(processor)
+
+  /** A source UPSERT event: `(id, value, seq, is_delete = false)`. */
+  private def upsert(id: Int, value: String, seq: Long): Row = Row(id, value, 
seq, false)
+
+  /** A source DELETE event: `(id, null, seq, is_delete = true)`. */
+  private def del(id: Int, seq: Long): Row = Row(id, null, seq, true)
+
+  /** The cdc-metadata struct value for a given `recordStartAt`. */
+  private def meta(recordStartAt: Long): Row = Row(recordStartAt)
+
+  /** A canonical target row `(id, value, startAt, endAt, 
meta(recordStartAt))`. */
+  private def targetRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt))
+
+  /** A canonical aux row `(id, value, startAt, endAt, meta(recordStartAt), 
deletedByBatchId)`. */
+  private def auxRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long,
+      deletedByBatchId: java.lang.Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt), deletedByBatchId)
+
+  /** Run a microbatch of source rows through the default handler. */
+  private def runBatch(batchId: Long)(rows: Row*): Unit =
+    exec.execute(microbatchOf(sourceSchema)(rows: _*), batchId)
+
+  /**
+   * Run `rows` as batch `batchId`, capture both tables, then replay the 
identical batch under the
+   * same `batchId` and assert both tables are byte-for-byte unchanged. Models 
a crash/redelivery
+   * where a committed microbatch is reprocessed.
+   */
+  private def assertReplayStable(batchId: Long)(rows: Row*): Unit = {
+    runBatch(batchId)(rows: _*)
+    val targetAfterFirst = targetTable.collect().toSeq
+    val auxAfterFirst = auxTable.collect().toSeq
+
+    runBatch(batchId)(rows: _*)
+    checkAnswer(targetTable, targetAfterFirst)
+    checkAnswer(auxTable, auxAfterFirst)
+  }
+
+  test("a record with a null sequencing value fails the microbatch without 
applying any changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(1, "bad", null, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 77L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_SEQUENCE",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "77",
+        "nullCount" -> "1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("a record with a null key fails the microbatch without applying any 
changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(null, "bad", 10L, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 7L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_KEY",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "7",
+        "nullKeyCounts" -> "`id`=1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("an empty microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)() // zero source rows
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an empty microbatch garbage-collects a stale aux row from a prior 
batch") {

Review Comment:
   I guess this covers the "both non-empty" case but we should still do a both 
empty case since that may happen on initial processing.



##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2ForeachBatchHandlerSuite.scala:
##########
@@ -0,0 +1,949 @@
+/*
+ * 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.spark.sql.pipelines.autocdc
+
+import org.scalatest.BeforeAndAfter
+
+import org.apache.spark.sql.{functions => F, AnalysisException, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+/**
+ * End-to-end unit tests for [[Scd2ForeachBatchHandler]]. Unlike the focused 
unit suites that
+ * exercise individual [[Scd2BatchProcessor]] stages in isolation, these drive 
the entire
+ * microbatch reconciliation pipeline - validation, preprocessing, 
affected-row pull-in from both
+ * side tables, decomposition, start/end reconciliation, aux routing, and the 
two `MERGE INTO`
+ * writes - through the public `execute` entrypoint against an in-memory v2 
catalog.
+ *
+ * They are the first place the cross-microbatch stateful behaviors 
(out-of-order arrivals, no-op
+ * run coalescing across batches, tombstone-driven suppression, and 
auxiliary-table garbage
+ * collection) can be observed against materialized target and auxiliary 
tables, so the idempotency
+ * / GC / cross-batch scenarios are emphasized here.
+ *
+ * The default flow tracks every persisted user column (`value`) under key 
`id`, sequences by
+ * `seq`, and treats `is_delete = true` rows as deletes.
+ */
+class Scd2ForeachBatchHandlerSuite
+    extends QueryTest
+    with SharedSparkSession
+    with BeforeAndAfter
+    with AutoCdcCatalogExecutionTestBase {
+
+  private val sourceSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add("seq", LongType)
+    .add("is_delete", BooleanType)
+
+  /** The SCD2 cdc-metadata struct carries a single `recordStartAt` field 
(unlike SCD1's two). */
+  private val scd2MetadataSchema: StructType = 
Scd2BatchProcessor.cdcMetadataColSchema(LongType)
+
+  /** Canonical SCD2 row schema: persisted user columns + framework start/end 
+ cdc metadata. */
+  private val canonicalSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add(Scd2BatchProcessor.startAtColName, LongType, nullable = true)
+    .add(Scd2BatchProcessor.endAtColName, LongType, nullable = true)
+    .add(AutoCdcReservedNames.cdcMetadataColName, scd2MetadataSchema, nullable 
= false)
+
+  /** Auxiliary table schema: canonical schema plus the aux-only 
logical-delete marker column. */
+  private val auxSchema = canonicalSchema
+    .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = true)
+
+  /** Target table schema is exactly the canonical schema. */
+  private val targetSchema = canonicalSchema
+
+  private val processor = Scd2BatchProcessor(
+    changeArgs = ChangeArgs(
+      keys = Seq(UnqualifiedColumnName("id")),
+      sequencing = F.col("seq"),
+      storedAsScdType = ScdType.Type2,
+      deleteCondition = Some(F.col("is_delete")),
+      // Persist only id + value; seq / is_delete are control columns and must 
not be stored.
+      columnSelection = Some(
+        ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("seq"), UnqualifiedColumnName("is_delete"))
+        )
+      )
+    ),
+    resolvedSequencingType = LongType
+  )
+
+  private def createAuxTable(seedRows: Row*): Unit =
+    createTable(defaultAuxIdent, defaultAuxTableIdentifier, auxSchema, 
seedRows: _*)
+
+  private def createTargetTable(seedRows: Row*): Unit =
+    createTable(defaultTargetIdent, defaultTargetTableIdentifier, 
targetSchema, seedRows: _*)
+
+  private def auxTable: DataFrame = 
spark.read.table(defaultAuxTableIdentifier.quotedString)
+
+  private def targetTable: DataFrame = 
spark.read.table(defaultTargetTableIdentifier.quotedString)
+
+  private def execWith(p: Scd2BatchProcessor): Scd2ForeachBatchHandler = 
Scd2ForeachBatchHandler(
+    batchProcessor = p,
+    auxiliaryTableIdentifier = defaultAuxTableIdentifier,
+    targetTableIdentifier = defaultTargetTableIdentifier
+  )
+
+  private def exec: Scd2ForeachBatchHandler = execWith(processor)
+
+  /** A source UPSERT event: `(id, value, seq, is_delete = false)`. */
+  private def upsert(id: Int, value: String, seq: Long): Row = Row(id, value, 
seq, false)
+
+  /** A source DELETE event: `(id, null, seq, is_delete = true)`. */
+  private def del(id: Int, seq: Long): Row = Row(id, null, seq, true)
+
+  /** The cdc-metadata struct value for a given `recordStartAt`. */
+  private def meta(recordStartAt: Long): Row = Row(recordStartAt)
+
+  /** A canonical target row `(id, value, startAt, endAt, 
meta(recordStartAt))`. */
+  private def targetRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt))
+
+  /** A canonical aux row `(id, value, startAt, endAt, meta(recordStartAt), 
deletedByBatchId)`. */
+  private def auxRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long,
+      deletedByBatchId: java.lang.Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt), deletedByBatchId)
+
+  /** Run a microbatch of source rows through the default handler. */
+  private def runBatch(batchId: Long)(rows: Row*): Unit =
+    exec.execute(microbatchOf(sourceSchema)(rows: _*), batchId)
+
+  /**
+   * Run `rows` as batch `batchId`, capture both tables, then replay the 
identical batch under the
+   * same `batchId` and assert both tables are byte-for-byte unchanged. Models 
a crash/redelivery
+   * where a committed microbatch is reprocessed.
+   */
+  private def assertReplayStable(batchId: Long)(rows: Row*): Unit = {
+    runBatch(batchId)(rows: _*)
+    val targetAfterFirst = targetTable.collect().toSeq
+    val auxAfterFirst = auxTable.collect().toSeq
+
+    runBatch(batchId)(rows: _*)
+    checkAnswer(targetTable, targetAfterFirst)
+    checkAnswer(auxTable, auxAfterFirst)
+  }
+
+  test("a record with a null sequencing value fails the microbatch without 
applying any changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(1, "bad", null, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 77L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_SEQUENCE",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "77",
+        "nullCount" -> "1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("a record with a null key fails the microbatch without applying any 
changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(null, "bad", 10L, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 7L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_KEY",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "7",
+        "nullKeyCounts" -> "`id`=1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("an empty microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)() // zero source rows
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an empty microbatch garbage-collects a stale aux row from a prior 
batch") {
+    // Batch 1: a late upsert logically deletes a tombstone, stamping 
deletedByBatchId=1.
+    createAuxTable()
+    createTargetTable()
+    runBatch(1L)(del(1, 20L))
+    runBatch(2L)(upsert(1, "x", 10L))
+    checkAnswer(auxTable, auxRow(1, null, 20L, 20L, 20L, 2L)) // tombstone 
stamped, not yet GC'd
+
+    // Batch 3: empty microbatch - no new work, but the GC clause still sweeps 
the aux table.
+    // The tombstone (deletedByBatchId=2, not equal to current batchId=3) is 
physically removed.
+    runBatch(3L)()
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "x", 10L, 20L, 10L))
+  }
+
+  test("inserting a new key creates an open current record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L))
+
+    // Open interval [10, null); nothing routed to the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("two updates to a key in one batch produce a closed record followed by 
the open record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), upsert(1, "b", 20L))
+
+    // a closes at b's start; b stays open. No hidden rows (every event 
changed the value).
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an insert and a later delete in the same batch leave a single closed 
record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), del(1, 20L))
+
+    // The closed interval [10, 20) already encodes the deletion boundary at 
20, so the delete's
+    // tombstone is redundant and dropped during reconciliation - nothing 
lands in the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an insert, update, delete, and re-insert for one key in a batch build 
the full history") {
+    createAuxTable()
+    createTargetTable()
+
+    // Unlike SCD1 - which would collapse these to the single latest state for 
the key - SCD2 keeps
+    // every event: each distinct value gets its own interval, the delete ends 
the active record,
+    // and the re-insert opens a fresh record after the deletion gap.
+    runBatch(1L)(
+      upsert(1, "a", 10L),
+      upsert(1, "b", 20L),
+      del(1, 30L),
+      upsert(1, "c", 40L)
+    )
+
+    // a [10, 20), b [20, 30) (closed by the delete), a deletion gap over [30, 
40), then c [40, ..).
+    // The delete leaves no tombstone: b's closed interval already carries the 
boundary at 30.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, 30L, 20L),
+        targetRow(1, "c", 40L, null, 40L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("repeating a key's value keeps one current record effective from its 
first occurrence") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), upsert(1, "a", 20L))
+
+    // The run [10, 20] coalesces: the visible tail carries the run-head 
START_AT (10) but the
+    // tail's own recordStartAt (20). The head becomes a hidden no-op row in 
the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 20L))
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+  }
+
+  test("deleting a key that has no current record leaves the dimension table 
empty") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(del(1, 5L))
+
+    // No preceding upsert closes on the boundary, so the tombstone survives 
as aux side state.
+    assert(targetTable.collect().isEmpty)
+    checkAnswer(auxTable, auxRow(1, null, 5L, 5L, 5L, null))
+  }
+
+  test("updating an existing key closes its current record and opens a new 
one") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)(upsert(1, "b", 20L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("deleting an existing key closes its current record with no open record 
remaining") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)(del(1, 20L))
+
+    // The resulting closed interval carries the deletion boundary; no 
tombstone needed.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an update preserves already-closed historical records") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 5L, 10L, 5L), // closed and settled well before the 
incoming event
+      targetRow(1, "b", 10L, null, 10L) // currently active
+    )
+
+    runBatch(3L)(upsert(1, "c", 20L))
+
+    // Only the active interval is pulled in and closed; the settled [5, 10) 
row is never touched.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 5L, 10L, 5L),
+        targetRow(1, "b", 10L, 20L, 10L),
+        targetRow(1, "c", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late event older than all existing history is inserted as the 
earliest record") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    // b arrives late with seq=5, strictly before the seeded interval's start.
+    runBatch(2L)(upsert(1, "b", 5L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "b", 5L, 10L, 5L),
+        targetRow(1, "a", 10L, null, 10L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late update landing inside an existing record splits it around the 
new value") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 10L, 20L, 10L),
+      targetRow(1, "c", 20L, null, 20L)
+    )
+
+    // b arrives late at seq=15, inside the closed [10, 20) interval.
+    runBatch(3L)(upsert(1, "b", 15L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 15L, 10L),
+        targetRow(1, "b", 15L, 20L, 15L),
+        targetRow(1, "c", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late delete landing inside an existing record shortens it to end at 
the deletion") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 10L, 30L, 10L),
+      targetRow(1, "b", 30L, null, 30L)
+    )
+
+    // Delete arrives late at seq=20, inside the closed [10, 30) interval.
+    runBatch(4L)(del(1, 20L))
+
+    // a is decomposed and re-closed at the delete boundary (20); b is 
unaffected. The delete is
+    // covered by the new closed interval [10, 20), so it leaves no aux 
tombstone.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 30L, null, 30L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("two late events in one batch each bisect a distinct closed target 
row") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 1L, 5L, 1L),
+      targetRow(1, "b", 5L, 10L, 5L),
+      targetRow(1, "c", 10L, 20L, 10L),
+      targetRow(1, "d", 20L, null, 20L)
+    )
+
+    // Late x at seq=7 bisects [5,10); late y at seq=15 bisects [10,20) -- 
both in the same batch.
+    runBatch(5L)(upsert(1, "x", 7L), upsert(1, "y", 15L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 1L, 5L, 1L),
+        targetRow(1, "b", 5L, 7L, 5L),
+        targetRow(1, "x", 7L, 10L, 7L),
+        targetRow(1, "c", 10L, 15L, 10L),
+        targetRow(1, "y", 15L, 20L, 15L),
+        targetRow(1, "d", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("re-inserting a key after it was deleted opens a new current record") {
+    createAuxTable(auxRow(1, null, 20L, 20L, 20L, null))
+    createTargetTable()
+
+    // Revival strictly after the recorded deletion at 20.
+    runBatch(5L)(upsert(1, "x", 30L))
+
+    // The revival opens a fresh interval; the deletion boundary at 20 stays 
in the aux table since
+    // no visible interval closes on it (there is a real gap [20, 30) where 
the key was absent).
+    checkAnswer(targetTable, targetRow(1, "x", 30L, null, 30L))
+    checkAnswer(auxTable, auxRow(1, null, 20L, 20L, 20L, null))
+  }
+
+  test("a value repeated across batches stays one record until a later change 
closes it") {
+    createAuxTable()
+    createTargetTable()
+
+    // Batch 1: establish the run head.
+    runBatch(1L)(upsert(1, "a", 10L))
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+
+    // Batch 2: a same-value upsert extends the run. The previously-visible 
head is demoted to the
+    // aux table and the new tail becomes the visible row (START_AT pinned to 
the run head, 10).
+    runBatch(2L)(upsert(1, "a", 20L))
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 20L))
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+
+    // Batch 3: a real value change closes the "a" run and opens "b". The 
hidden head is retained
+    // as aux side state for any future bisecting event.
+    runBatch(3L)(upsert(1, "b", 30L))
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 30L, 20L),
+        targetRow(1, "b", 30L, null, 30L)
+      )
+    )
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+  }
+
+  test("a late event arriving within an unchanged period splits the 
surrounding history") {
+    createAuxTable()
+    createTargetTable()
+
+    // Build the Alice run [5, 10, 15] then Charlie at 20.
+    runBatch(1L)(upsert(1, "Alice", 5L), upsert(1, "Alice", 10L), upsert(1, 
"Alice", 15L))
+    runBatch(2L)(upsert(1, "Charlie", 20L))
+
+    // Alice's run is [5, 20); the visible tail is the latest Alice event (15) 
with START_AT=5.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "Alice", 5L, 20L, 15L),
+        targetRow(1, "Charlie", 20L, null, 20L)
+      )
+    )
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "Alice", 5L, null, 5L, null),
+        auxRow(1, "Alice", 5L, null, 10L, null)
+      )
+    )
+
+    // Late Bob at 12 splits the Alice run: Alice [5, 12) (tail now the 10 
event), Bob [12, 15),
+    // Alice [15, 20) (a fresh size-1 run).
+    runBatch(3L)(upsert(1, "Bob", 12L))
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "Alice", 5L, 12L, 10L),
+        targetRow(1, "Bob", 12L, 15L, 12L),
+        targetRow(1, "Alice", 15L, 20L, 15L),
+        targetRow(1, "Charlie", 20L, null, 20L)
+      )
+    )
+    // The hidden run head (recordStartAt=5) survives as side state. The other 
previously-hidden
+    // no-op (recordStartAt=10) is promoted to the visible tail of [5, 12); it 
leaves the aux table
+    // logically (stamped with this batch's id), to be physically 
garbage-collected by a later
+    // unrelated batch.
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "Alice", 5L, null, 5L, null),
+        auxRow(1, "Alice", 5L, null, 10L, 3L)
+      )
+    )
+  }
+
+  test("reprocessing an update microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    assertReplayStable(2L)(upsert(1, "b", 20L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("reprocessing a delete microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    assertReplayStable(2L)(del(1, 20L))
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("reprocessing a microbatch of repeated values leaves both tables 
unchanged") {
+    createAuxTable()
+    createTargetTable()
+
+    assertReplayStable(1L)(upsert(1, "a", 10L), upsert(1, "a", 20L), upsert(1, 
"a", 30L))
+
+    // A single run of same-value events at sequences 10, 20, 30; the latest 
(30) is the visible
+    // tail (open from startAt 10), the earlier two are hidden.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 30L))
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "a", 10L, null, 10L, null),
+        auxRow(1, "a", 10L, null, 20L, null)
+      )
+    )
+  }
+
+  test("reprocessing a delete of an unknown key leaves both tables unchanged") 
{
+    createAuxTable()
+    createTargetTable()
+
+    assertReplayStable(7L)(del(1, 5L))
+
+    assert(targetTable.collect().isEmpty)
+    checkAnswer(auxTable, auxRow(1, null, 5L, 5L, 5L, null))
+  }
+
+  test("byte-identical duplicate events in one microbatch collapse to a single 
record") {
+    createAuxTable()
+    createTargetTable()
+
+    // Two fully identical events (same key, value, and sequence). 
Preprocessing keeps both 1:1;
+    // because they share a recordStartAt, reconciliation collapses them to 
one. The result is a

Review Comment:
   Is it "byte-identical" from the test name that's the collapse condition, or 
do just the key and recordStartAt have to match? (In either case we should bake 
in the appropriate test behavior)



##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd2ForeachBatchHandlerSuite.scala:
##########
@@ -0,0 +1,949 @@
+/*
+ * 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.spark.sql.pipelines.autocdc
+
+import org.scalatest.BeforeAndAfter
+
+import org.apache.spark.sql.{functions => F, AnalysisException, QueryTest, Row}
+import org.apache.spark.sql.classic.DataFrame
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.test.SharedSparkSession
+import org.apache.spark.sql.types._
+
+/**
+ * End-to-end unit tests for [[Scd2ForeachBatchHandler]]. Unlike the focused 
unit suites that
+ * exercise individual [[Scd2BatchProcessor]] stages in isolation, these drive 
the entire
+ * microbatch reconciliation pipeline - validation, preprocessing, 
affected-row pull-in from both
+ * side tables, decomposition, start/end reconciliation, aux routing, and the 
two `MERGE INTO`
+ * writes - through the public `execute` entrypoint against an in-memory v2 
catalog.
+ *
+ * They are the first place the cross-microbatch stateful behaviors 
(out-of-order arrivals, no-op
+ * run coalescing across batches, tombstone-driven suppression, and 
auxiliary-table garbage
+ * collection) can be observed against materialized target and auxiliary 
tables, so the idempotency
+ * / GC / cross-batch scenarios are emphasized here.
+ *
+ * The default flow tracks every persisted user column (`value`) under key 
`id`, sequences by
+ * `seq`, and treats `is_delete = true` rows as deletes.
+ */
+class Scd2ForeachBatchHandlerSuite
+    extends QueryTest
+    with SharedSparkSession
+    with BeforeAndAfter
+    with AutoCdcCatalogExecutionTestBase {
+
+  private val sourceSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add("seq", LongType)
+    .add("is_delete", BooleanType)
+
+  /** The SCD2 cdc-metadata struct carries a single `recordStartAt` field 
(unlike SCD1's two). */
+  private val scd2MetadataSchema: StructType = 
Scd2BatchProcessor.cdcMetadataColSchema(LongType)
+
+  /** Canonical SCD2 row schema: persisted user columns + framework start/end 
+ cdc metadata. */
+  private val canonicalSchema = new StructType()
+    .add("id", IntegerType)
+    .add("value", StringType)
+    .add(Scd2BatchProcessor.startAtColName, LongType, nullable = true)
+    .add(Scd2BatchProcessor.endAtColName, LongType, nullable = true)
+    .add(AutoCdcReservedNames.cdcMetadataColName, scd2MetadataSchema, nullable 
= false)
+
+  /** Auxiliary table schema: canonical schema plus the aux-only 
logical-delete marker column. */
+  private val auxSchema = canonicalSchema
+    .add(Scd2BatchProcessor.deletedByBatchIdColName, LongType, nullable = true)
+
+  /** Target table schema is exactly the canonical schema. */
+  private val targetSchema = canonicalSchema
+
+  private val processor = Scd2BatchProcessor(
+    changeArgs = ChangeArgs(
+      keys = Seq(UnqualifiedColumnName("id")),
+      sequencing = F.col("seq"),
+      storedAsScdType = ScdType.Type2,
+      deleteCondition = Some(F.col("is_delete")),
+      // Persist only id + value; seq / is_delete are control columns and must 
not be stored.
+      columnSelection = Some(
+        ColumnSelection.ExcludeColumns(
+          Seq(UnqualifiedColumnName("seq"), UnqualifiedColumnName("is_delete"))
+        )
+      )
+    ),
+    resolvedSequencingType = LongType
+  )
+
+  private def createAuxTable(seedRows: Row*): Unit =
+    createTable(defaultAuxIdent, defaultAuxTableIdentifier, auxSchema, 
seedRows: _*)
+
+  private def createTargetTable(seedRows: Row*): Unit =
+    createTable(defaultTargetIdent, defaultTargetTableIdentifier, 
targetSchema, seedRows: _*)
+
+  private def auxTable: DataFrame = 
spark.read.table(defaultAuxTableIdentifier.quotedString)
+
+  private def targetTable: DataFrame = 
spark.read.table(defaultTargetTableIdentifier.quotedString)
+
+  private def execWith(p: Scd2BatchProcessor): Scd2ForeachBatchHandler = 
Scd2ForeachBatchHandler(
+    batchProcessor = p,
+    auxiliaryTableIdentifier = defaultAuxTableIdentifier,
+    targetTableIdentifier = defaultTargetTableIdentifier
+  )
+
+  private def exec: Scd2ForeachBatchHandler = execWith(processor)
+
+  /** A source UPSERT event: `(id, value, seq, is_delete = false)`. */
+  private def upsert(id: Int, value: String, seq: Long): Row = Row(id, value, 
seq, false)
+
+  /** A source DELETE event: `(id, null, seq, is_delete = true)`. */
+  private def del(id: Int, seq: Long): Row = Row(id, null, seq, true)
+
+  /** The cdc-metadata struct value for a given `recordStartAt`. */
+  private def meta(recordStartAt: Long): Row = Row(recordStartAt)
+
+  /** A canonical target row `(id, value, startAt, endAt, 
meta(recordStartAt))`. */
+  private def targetRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt))
+
+  /** A canonical aux row `(id, value, startAt, endAt, meta(recordStartAt), 
deletedByBatchId)`. */
+  private def auxRow(
+      id: Int,
+      value: String,
+      startAt: java.lang.Long,
+      endAt: java.lang.Long,
+      recordStartAt: Long,
+      deletedByBatchId: java.lang.Long): Row =
+    Row(id, value, startAt, endAt, meta(recordStartAt), deletedByBatchId)
+
+  /** Run a microbatch of source rows through the default handler. */
+  private def runBatch(batchId: Long)(rows: Row*): Unit =
+    exec.execute(microbatchOf(sourceSchema)(rows: _*), batchId)
+
+  /**
+   * Run `rows` as batch `batchId`, capture both tables, then replay the 
identical batch under the
+   * same `batchId` and assert both tables are byte-for-byte unchanged. Models 
a crash/redelivery
+   * where a committed microbatch is reprocessed.
+   */
+  private def assertReplayStable(batchId: Long)(rows: Row*): Unit = {
+    runBatch(batchId)(rows: _*)
+    val targetAfterFirst = targetTable.collect().toSeq
+    val auxAfterFirst = auxTable.collect().toSeq
+
+    runBatch(batchId)(rows: _*)
+    checkAnswer(targetTable, targetAfterFirst)
+    checkAnswer(auxTable, auxAfterFirst)
+  }
+
+  test("a record with a null sequencing value fails the microbatch without 
applying any changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(1, "bad", null, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 77L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_SEQUENCE",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "77",
+        "nullCount" -> "1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("a record with a null key fails the microbatch without applying any 
changes") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "old", 10L, null, 10L))
+
+    val batch = microbatchOf(sourceSchema)(Row(null, "bad", 10L, false))
+
+    checkError(
+      exception = intercept[AnalysisException] {
+        exec.execute(batch, batchId = 7L)
+      },
+      condition = "AUTOCDC_MICROBATCH_VALIDATION.NULL_KEY",
+      sqlState = "22000",
+      parameters = Map(
+        "tableName" -> defaultTargetTableIdentifier.quotedString,
+        "batchId" -> "7",
+        "nullKeyCounts" -> "`id`=1"
+      )
+    )
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "old", 10L, null, 10L))
+  }
+
+  test("an empty microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)() // zero source rows
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an empty microbatch garbage-collects a stale aux row from a prior 
batch") {
+    // Batch 1: a late upsert logically deletes a tombstone, stamping 
deletedByBatchId=1.
+    createAuxTable()
+    createTargetTable()
+    runBatch(1L)(del(1, 20L))
+    runBatch(2L)(upsert(1, "x", 10L))
+    checkAnswer(auxTable, auxRow(1, null, 20L, 20L, 20L, 2L)) // tombstone 
stamped, not yet GC'd
+
+    // Batch 3: empty microbatch - no new work, but the GC clause still sweeps 
the aux table.
+    // The tombstone (deletedByBatchId=2, not equal to current batchId=3) is 
physically removed.
+    runBatch(3L)()
+
+    assert(auxTable.collect().isEmpty)
+    checkAnswer(targetTable, targetRow(1, "x", 10L, 20L, 10L))
+  }
+
+  test("inserting a new key creates an open current record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L))
+
+    // Open interval [10, null); nothing routed to the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("two updates to a key in one batch produce a closed record followed by 
the open record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), upsert(1, "b", 20L))
+
+    // a closes at b's start; b stays open. No hidden rows (every event 
changed the value).
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an insert and a later delete in the same batch leave a single closed 
record") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), del(1, 20L))
+
+    // The closed interval [10, 20) already encodes the deletion boundary at 
20, so the delete's
+    // tombstone is redundant and dropped during reconciliation - nothing 
lands in the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an insert, update, delete, and re-insert for one key in a batch build 
the full history") {
+    createAuxTable()
+    createTargetTable()
+
+    // Unlike SCD1 - which would collapse these to the single latest state for 
the key - SCD2 keeps
+    // every event: each distinct value gets its own interval, the delete ends 
the active record,
+    // and the re-insert opens a fresh record after the deletion gap.
+    runBatch(1L)(
+      upsert(1, "a", 10L),
+      upsert(1, "b", 20L),
+      del(1, 30L),
+      upsert(1, "c", 40L)
+    )
+
+    // a [10, 20), b [20, 30) (closed by the delete), a deletion gap over [30, 
40), then c [40, ..).
+    // The delete leaves no tombstone: b's closed interval already carries the 
boundary at 30.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, 30L, 20L),
+        targetRow(1, "c", 40L, null, 40L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("repeating a key's value keeps one current record effective from its 
first occurrence") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(upsert(1, "a", 10L), upsert(1, "a", 20L))
+
+    // The run [10, 20] coalesces: the visible tail carries the run-head 
START_AT (10) but the
+    // tail's own recordStartAt (20). The head becomes a hidden no-op row in 
the aux table.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 20L))
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+  }
+
+  test("deleting a key that has no current record leaves the dimension table 
empty") {
+    createAuxTable()
+    createTargetTable()
+
+    runBatch(1L)(del(1, 5L))
+
+    // No preceding upsert closes on the boundary, so the tombstone survives 
as aux side state.
+    assert(targetTable.collect().isEmpty)
+    checkAnswer(auxTable, auxRow(1, null, 5L, 5L, 5L, null))
+  }
+
+  test("updating an existing key closes its current record and opens a new 
one") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)(upsert(1, "b", 20L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("deleting an existing key closes its current record with no open record 
remaining") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    runBatch(2L)(del(1, 20L))
+
+    // The resulting closed interval carries the deletion boundary; no 
tombstone needed.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("an update preserves already-closed historical records") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 5L, 10L, 5L), // closed and settled well before the 
incoming event
+      targetRow(1, "b", 10L, null, 10L) // currently active
+    )
+
+    runBatch(3L)(upsert(1, "c", 20L))
+
+    // Only the active interval is pulled in and closed; the settled [5, 10) 
row is never touched.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 5L, 10L, 5L),
+        targetRow(1, "b", 10L, 20L, 10L),
+        targetRow(1, "c", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late event older than all existing history is inserted as the 
earliest record") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    // b arrives late with seq=5, strictly before the seeded interval's start.
+    runBatch(2L)(upsert(1, "b", 5L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "b", 5L, 10L, 5L),
+        targetRow(1, "a", 10L, null, 10L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late update landing inside an existing record splits it around the 
new value") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 10L, 20L, 10L),
+      targetRow(1, "c", 20L, null, 20L)
+    )
+
+    // b arrives late at seq=15, inside the closed [10, 20) interval.
+    runBatch(3L)(upsert(1, "b", 15L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 15L, 10L),
+        targetRow(1, "b", 15L, 20L, 15L),
+        targetRow(1, "c", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("a late delete landing inside an existing record shortens it to end at 
the deletion") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 10L, 30L, 10L),
+      targetRow(1, "b", 30L, null, 30L)
+    )
+
+    // Delete arrives late at seq=20, inside the closed [10, 30) interval.
+    runBatch(4L)(del(1, 20L))
+
+    // a is decomposed and re-closed at the delete boundary (20); b is 
unaffected. The delete is
+    // covered by the new closed interval [10, 20), so it leaves no aux 
tombstone.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 30L, null, 30L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("two late events in one batch each bisect a distinct closed target 
row") {
+    createAuxTable()
+    createTargetTable(
+      targetRow(1, "a", 1L, 5L, 1L),
+      targetRow(1, "b", 5L, 10L, 5L),
+      targetRow(1, "c", 10L, 20L, 10L),
+      targetRow(1, "d", 20L, null, 20L)
+    )
+
+    // Late x at seq=7 bisects [5,10); late y at seq=15 bisects [10,20) -- 
both in the same batch.
+    runBatch(5L)(upsert(1, "x", 7L), upsert(1, "y", 15L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 1L, 5L, 1L),
+        targetRow(1, "b", 5L, 7L, 5L),
+        targetRow(1, "x", 7L, 10L, 7L),
+        targetRow(1, "c", 10L, 15L, 10L),
+        targetRow(1, "y", 15L, 20L, 15L),
+        targetRow(1, "d", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("re-inserting a key after it was deleted opens a new current record") {
+    createAuxTable(auxRow(1, null, 20L, 20L, 20L, null))
+    createTargetTable()
+
+    // Revival strictly after the recorded deletion at 20.
+    runBatch(5L)(upsert(1, "x", 30L))
+
+    // The revival opens a fresh interval; the deletion boundary at 20 stays 
in the aux table since
+    // no visible interval closes on it (there is a real gap [20, 30) where 
the key was absent).
+    checkAnswer(targetTable, targetRow(1, "x", 30L, null, 30L))
+    checkAnswer(auxTable, auxRow(1, null, 20L, 20L, 20L, null))
+  }
+
+  test("a value repeated across batches stays one record until a later change 
closes it") {
+    createAuxTable()
+    createTargetTable()
+
+    // Batch 1: establish the run head.
+    runBatch(1L)(upsert(1, "a", 10L))
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+
+    // Batch 2: a same-value upsert extends the run. The previously-visible 
head is demoted to the
+    // aux table and the new tail becomes the visible row (START_AT pinned to 
the run head, 10).
+    runBatch(2L)(upsert(1, "a", 20L))
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 20L))
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+
+    // Batch 3: a real value change closes the "a" run and opens "b". The 
hidden head is retained
+    // as aux side state for any future bisecting event.
+    runBatch(3L)(upsert(1, "b", 30L))
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 30L, 20L),
+        targetRow(1, "b", 30L, null, 30L)
+      )
+    )
+    checkAnswer(auxTable, auxRow(1, "a", 10L, null, 10L, null))
+  }
+
+  test("a late event arriving within an unchanged period splits the 
surrounding history") {
+    createAuxTable()
+    createTargetTable()
+
+    // Build the Alice run [5, 10, 15] then Charlie at 20.
+    runBatch(1L)(upsert(1, "Alice", 5L), upsert(1, "Alice", 10L), upsert(1, 
"Alice", 15L))
+    runBatch(2L)(upsert(1, "Charlie", 20L))
+
+    // Alice's run is [5, 20); the visible tail is the latest Alice event (15) 
with START_AT=5.
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "Alice", 5L, 20L, 15L),
+        targetRow(1, "Charlie", 20L, null, 20L)
+      )
+    )
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "Alice", 5L, null, 5L, null),
+        auxRow(1, "Alice", 5L, null, 10L, null)
+      )
+    )
+
+    // Late Bob at 12 splits the Alice run: Alice [5, 12) (tail now the 10 
event), Bob [12, 15),
+    // Alice [15, 20) (a fresh size-1 run).
+    runBatch(3L)(upsert(1, "Bob", 12L))
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "Alice", 5L, 12L, 10L),
+        targetRow(1, "Bob", 12L, 15L, 12L),
+        targetRow(1, "Alice", 15L, 20L, 15L),
+        targetRow(1, "Charlie", 20L, null, 20L)
+      )
+    )
+    // The hidden run head (recordStartAt=5) survives as side state. The other 
previously-hidden
+    // no-op (recordStartAt=10) is promoted to the visible tail of [5, 12); it 
leaves the aux table
+    // logically (stamped with this batch's id), to be physically 
garbage-collected by a later
+    // unrelated batch.
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "Alice", 5L, null, 5L, null),
+        auxRow(1, "Alice", 5L, null, 10L, 3L)
+      )
+    )
+  }
+
+  test("reprocessing an update microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    assertReplayStable(2L)(upsert(1, "b", 20L))
+
+    checkAnswer(
+      targetTable,
+      Seq(
+        targetRow(1, "a", 10L, 20L, 10L),
+        targetRow(1, "b", 20L, null, 20L)
+      )
+    )
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("reprocessing a delete microbatch leaves both tables unchanged") {
+    createAuxTable()
+    createTargetTable(targetRow(1, "a", 10L, null, 10L))
+
+    assertReplayStable(2L)(del(1, 20L))
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, 20L, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("reprocessing a microbatch of repeated values leaves both tables 
unchanged") {
+    createAuxTable()
+    createTargetTable()
+
+    assertReplayStable(1L)(upsert(1, "a", 10L), upsert(1, "a", 20L), upsert(1, 
"a", 30L))
+
+    // A single run of same-value events at sequences 10, 20, 30; the latest 
(30) is the visible
+    // tail (open from startAt 10), the earlier two are hidden.
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 30L))
+    checkAnswer(
+      auxTable,
+      Seq(
+        auxRow(1, "a", 10L, null, 10L, null),
+        auxRow(1, "a", 10L, null, 20L, null)
+      )
+    )
+  }
+
+  test("reprocessing a delete of an unknown key leaves both tables unchanged") 
{
+    createAuxTable()
+    createTargetTable()
+
+    assertReplayStable(7L)(del(1, 5L))
+
+    assert(targetTable.collect().isEmpty)
+    checkAnswer(auxTable, auxRow(1, null, 5L, 5L, 5L, null))
+  }
+
+  test("byte-identical duplicate events in one microbatch collapse to a single 
record") {
+    createAuxTable()
+    createTargetTable()
+
+    // Two fully identical events (same key, value, and sequence). 
Preprocessing keeps both 1:1;
+    // because they share a recordStartAt, reconciliation collapses them to 
one. The result is a
+    // single open record - and notably no hidden aux row, unlike a run of 
same-value events at
+    // *distinct* sequences (where the non-tail members are retained as side 
state).
+    runBatch(1L)(upsert(1, "a", 10L), upsert(1, "a", 10L))
+
+    checkAnswer(targetTable, targetRow(1, "a", 10L, null, 10L))
+    assert(auxTable.collect().isEmpty)
+  }
+
+  test("redelivering the same event in a later microbatch leaves both tables 
unchanged") {

Review Comment:
   As above, we should have a bit more coverage here to identify the exact 
"same event" condition (which hopefully uses the same logic both within and 
across batches)



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