AnishMahto commented on code in PR #55991:
URL: https://github.com/apache/spark/pull/55991#discussion_r3283685732


##########
sql/pipelines/src/test/scala/org/apache/spark/sql/pipelines/autocdc/Scd1BatchProcessorSuite.scala:
##########
@@ -0,0 +1,625 @@
+/*
+ * 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.apache.spark.SparkFunSuite
+import org.apache.spark.sql.{functions => F, AnalysisException, 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._
+
+class Scd1BatchProcessorSuite extends SparkFunSuite with SharedSparkSession {
+
+  /**
+   * Test Schema for a microbatch that already has the SCD1 CDC metadata 
column projected.
+   */
+  private val microbatchWithCdcMetadataSchema: StructType = new StructType()
+    .add("id", IntegerType)
+    .add("name", StringType)
+    .add("age", IntegerType)
+    .add(
+      Scd1BatchProcessor.cdcMetadataColName,
+      new StructType()
+        .add(Scd1BatchProcessor.cdcDeleteSequenceFieldName, LongType)
+        .add(Scd1BatchProcessor.cdcUpsertSequenceFieldName, LongType)
+    )
+
+  /** Build a microbatch [[DataFrame]] from explicit rows and an explicit 
schema. */
+  private def microbatchOf(schema: StructType)(rows: Row*): DataFrame =
+    spark.createDataFrame(spark.sparkContext.parallelize(rows), schema)
+
+  /**
+   * Returns the `(name, dataType)` pairs of `schema`'s fields. Used to 
compare two schemas for
+   * structural equivalence while deliberately ignoring nullability and 
metadata, which can shift
+   * benignly when columns are unpacked from a struct.
+   */
+  private def columnNamesAndDataTypes(schema: StructType): Seq[(String, 
DataType)] =
+    schema.fields.map(f => (f.name, f.dataType)).toSeq
+
+  test("deduplicateMicrobatch keeps only the row with the largest sequence 
value per key") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "first"),
+      Row(1, 30L, "winner"),
+      Row(1, 20L, "middle")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.deduplicateMicrobatch(batch),
+      expectedAnswer = Row(1, 30L, "winner")
+    )
+  }
+
+  test("deduplicateMicrobatch processes multiple keys independently") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "a1"),
+      Row(2, 50L, "b1-winner"),
+      Row(1, 20L, "a2-winner"),
+      Row(2, 40L, "b2-loser"),
+      Row(3, 1L, "c1-only")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.deduplicateMicrobatch(batch),
+      expectedAnswer = Seq(
+        Row(1, 20L, "a2-winner"),
+        Row(2, 50L, "b1-winner"),
+        Row(3, 1L, "c1-only")
+      )
+    )
+  }
+
+  test("deduplicateMicrobatch carries non-key, non-sequence columns from the 
winning row") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("name", StringType)
+      .add("amount", IntegerType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "old-name", 100),
+      Row(1, 20L, "winning-name", 200)
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // All non-key columns must come from the row with the largest sequence 
value, never
+    // a mix of values from multiple rows.
+    checkAnswer(
+      df = processor.deduplicateMicrobatch(batch),
+      expectedAnswer = Row(1, 20L, "winning-name", 200)
+    )
+  }
+
+  test("deduplicateMicrobatch supports composite (multi-column) keys") {
+    val schema = new StructType()
+      .add("region", StringType)
+      .add("customer_id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row("US", 1, 10L, "us1-old"),
+      Row("US", 1, 20L, "us1-new"),
+      // Same customer_id as above but different region: independent group.
+      Row("EU", 1, 5L, "eu1-only"),
+      // Same region as above but different customer_id: independent group.
+      Row("US", 2, 99L, "us2-only")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("region"), 
UnqualifiedColumnName("customer_id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.deduplicateMicrobatch(batch),
+      expectedAnswer = Seq(
+        Row("US", 1, 20L, "us1-new"),
+        Row("EU", 1, 5L, "eu1-only"),
+        Row("US", 2, 99L, "us2-only")
+      )
+    )
+  }
+
+  test("deduplicateMicrobatch supports literal-dot column names") {
+    val schema = new StructType()
+      .add("user.id", IntegerType)
+      .add("seq", LongType)
+      .add("event.value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "old"),
+      Row(1, 20L, "new")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("`user.id`")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.deduplicateMicrobatch(batch),
+      expectedAnswer = Row(1, 20L, "new")
+    )
+  }
+
+  test("deduplicateMicrobatch preserves the input column names, types, and 
ordering") {
+    val schema = new StructType()
+      .add("a", StringType)
+      .add("id", IntegerType)
+      .add("z", DoubleType)
+      .add("seq", LongType)
+      .add("flag", BooleanType)
+
+    val batch = microbatchOf(schema)(
+      Row("a1", 1, 1.5, 10L, true),
+      Row("a2", 1, 2.5, 20L, false)
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // Field names and dataTypes must match the input exactly, in the original 
order.
+    assert(
+      columnNamesAndDataTypes(processor.deduplicateMicrobatch(batch).schema) ==
+        columnNamesAndDataTypes(schema))
+  }
+
+  test("deduplicateMicrobatch returns an empty DataFrame with preserved 
schema") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)()
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.deduplicateMicrobatch(batch)
+    assert(result.collect().isEmpty)
+    assert(columnNamesAndDataTypes(result.schema) == 
columnNamesAndDataTypes(schema))
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata classifies each row as a delete or 
an upsert " +
+    "per deleteCondition") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("is_delete", BooleanType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, false),
+      Row(2, 20L, true),
+      Row(3, 30L, false),
+      Row(4, 40L, true)
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1,
+        deleteCondition = Some(F.col("is_delete") === true)
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    // Mutual-exclusivity invariant: each row's _cdc_metadata struct has 
exactly one of
+    // (deleteSequence, upsertSequence) non-null, and the non-null side 
carries the row's
+    // sequence value.
+    checkAnswer(
+      df = processor.extendMicrobatchRowsWithCdcMetadata(batch),
+      expectedAnswer = Seq(
+        Row(1, 10L, false, Row(null, 10L)),
+        Row(2, 20L, true, Row(20L, null)),
+        Row(3, 30L, false, Row(null, 30L)),
+        Row(4, 40L, true, Row(40L, null))
+      )
+    )
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata treats every row as an upsert " +
+    "when deleteCondition is None") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "a"),
+      Row(2, 20L, "b")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1,
+        deleteCondition = None
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    checkAnswer(
+      df = processor.extendMicrobatchRowsWithCdcMetadata(batch),
+      expectedAnswer = Seq(
+        Row(1, 10L, "a", Row(null, 10L)),
+        Row(2, 20L, "b", Row(null, 20L))
+      )
+    )
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata appends CDC metadata as the last 
column") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      .add("seq", LongType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10L, "a")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val result = processor.extendMicrobatchRowsWithCdcMetadata(batch)
+
+    // Original columns are preserved in their original order, with CDC 
metadata appended at
+    // the very end.
+    assert(result.schema.fieldNames.toSeq ==
+      schema.fieldNames.toSeq :+ Scd1BatchProcessor.cdcMetadataColName)
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata casts delete / upsert sequence 
fields to " +
+    "resolvedSequencingType") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      // Microbatch's sequencing column is IntegerType, but the flow's 
resolved sequencing type
+      // will be LongType. This should be upcasted in the projected CDC 
metadata column.
+      .add("seq", IntegerType)
+      .add("value", StringType)
+
+    val batch = microbatchOf(schema)(
+      Row(1, 10, "a")
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val resultDf = processor.extendMicrobatchRowsWithCdcMetadata(batch)
+
+    val cdcMetadataDataType =
+      
resultDf.schema(Scd1BatchProcessor.cdcMetadataColName).dataType.asInstanceOf[StructType]
+    assert(columnNamesAndDataTypes(cdcMetadataDataType) == Seq(
+      Scd1BatchProcessor.cdcDeleteSequenceFieldName -> LongType,
+      Scd1BatchProcessor.cdcUpsertSequenceFieldName -> LongType))
+
+    // The cast must also succeed at runtime: upsertSequence is materialized 
as a Long value, not
+    // an Int.
+    checkAnswer(
+      df = resultDf,
+      expectedAnswer = Row(1, 10, "a", Row(null, 10L))
+    )
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata fails fast when the microbatch's 
sequencing column " +
+    "is incompatible with resolvedSequencingType") {
+    val schema = new StructType()
+      .add("id", IntegerType)
+      // Microbatch's sequencing column is a struct, whereas the flow's 
resolved sequencing type
+      // will be LongType. These are incompatible and should throw.
+      .add(
+        "seq",
+        new StructType()
+          .add("major", LongType)
+          .add("minor", LongType))
+
+    val batch = microbatchOf(schema)(
+      Row(1, Row(1L, 0L))
+    )
+
+    val processor = Scd1BatchProcessor(
+      changeArgs = ChangeArgs(
+        keys = Seq(UnqualifiedColumnName("id")),
+        sequencing = F.col("seq"),
+        storedAsScdType = ScdType.Type1
+      ),
+      resolvedSequencingType = LongType
+    )
+
+    val ex = intercept[AnalysisException] {
+      // .schema forces analysis of the underlying logical plan, surfacing the 
invalid cast.
+      processor.extendMicrobatchRowsWithCdcMetadata(batch).schema
+    }
+    assert(ex.getCondition == "DATATYPE_MISMATCH.CAST_WITHOUT_SUGGESTION")
+  }
+
+  test("extendMicrobatchRowsWithCdcMetadata rejects a microbatch that already 
contains the " +
+    "reserved CDC metadata column") {
+    withSQLConf(SQLConf.CASE_SENSITIVE.key -> "true") {
+      val schema = new StructType()
+        .add("id", IntegerType)
+        .add("seq", LongType)
+        .add(Scd1BatchProcessor.cdcMetadataColName, StringType)
+
+      val batch = microbatchOf(schema)(
+        Row(1, 10L, "user-supplied")
+      )
+
+      val processor = Scd1BatchProcessor(
+        changeArgs = ChangeArgs(
+          keys = Seq(UnqualifiedColumnName("id")),
+          sequencing = F.col("seq"),
+          storedAsScdType = ScdType.Type1
+        ),
+        resolvedSequencingType = LongType
+      )
+
+      checkError(
+        exception = intercept[AnalysisException] {
+          processor.extendMicrobatchRowsWithCdcMetadata(batch)
+        },
+        condition = "AUTOCDC_RESERVED_COLUMN_NAME_CONFLICT",
+        sqlState = "42710",
+        parameters = Map(
+          "caseSensitivity" -> CaseSensitivityLabels.CaseSensitive,
+          "columnName" -> Scd1BatchProcessor.cdcMetadataColName,
+          "schemaName" -> "microbatch",
+          "reservedColumnName" -> Scd1BatchProcessor.cdcMetadataColName
+        )
+      )
+    }
+  }
+
+  test("projectTargetColumnsOntoMicrobatch keeps every user column and the CDC 
metadata column " +

Review Comment:
   Added a test for case-insensitive.
   
   Not adding a test for `IncludeColumns(Seq())` because its not super 
meaningful. As discussed in other thread, it will be invalid for users to 
exclude key columns, and its also validated at construction time that key 
column list is non-empty. So `IncludeColumns(Seq())` can never happen in 
practice when everything is hooked up.



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