[Spark] Minor refactor to ManagedCommitBaseSuite utility - add commen…

…ts (delta-io#2821)

## Description

Minor refactor to ManagedCommitBaseSuite utility - add comments.

## How was this patch tested?

Existing UTs

## Does this PR introduce _any_ user-facing changes?

No

spark/src/test/scala/org/apache/spark/sql/delta/DeltaHistoryManagerSuite.scala

@@ -636,5 +636,5 @@ class DeltaHistoryManagerSuite extends DeltaHistoryManagerBase {
 }
 
 class ManagedCommitFill1DeltaHistoryManagerSuite extends DeltaHistoryManagerSuite {
-  override val managedCommitBackfillBatchSize: Option[Int] = Some(1)
+  override def managedCommitBackfillBatchSize: Option[Int] = Some(1)
 }

spark/src/test/scala/org/apache/spark/sql/delta/DeltaTimeTravelSuite.scala

@@ -765,5 +765,5 @@ class DeltaTimeTravelSuite extends QueryTest
 }
 
 class ManagedCommitFill1DeltaTimeTravelSuite extends DeltaTimeTravelSuite {
-  override val managedCommitBackfillBatchSize: Option[Int] = Some(1)
+  override def managedCommitBackfillBatchSize: Option[Int] = Some(1)
 }

spark/src/test/scala/org/apache/spark/sql/delta/managedcommit/ManagedCommitTestUtils.scala

@@ -28,6 +28,7 @@ import org.apache.spark.sql.test.SharedSparkSession
 trait ManagedCommitTestUtils
   extends DeltaTestUtilsBase { self: SparkFunSuite with SharedSparkSession =>
 
+  /** Run the test with different backfill batch sizes: 1, 2, 10 */
   def testWithDifferentBackfillInterval(testName: String)(f: Int => Unit): Unit = {
     Seq(1, 2, 10).foreach { backfillBatchSize =>
       test(s"$testName [Backfill batch size: $backfillBatchSize]") {
@@ -39,8 +40,11 @@ trait ManagedCommitTestUtils
     }
   }
 
-  def testWithDifferentBackfillIntervalOptional(
-      testName: String)(f: Option[Int] => Unit): Unit = {
+  /** Run the test with:
+   * 1. Without managed-commits
+   * 2. With managed-commits with different backfill batch sizes
+   */
+  def testWithDifferentBackfillIntervalOptional(testName: String)(f: Option[Int] => Unit): Unit = {
     test(s"$testName [Backfill batch size: None]") {
       f(None)
     }
@@ -129,28 +133,34 @@ class TrackingCommitStore(delegatingCommitStore: InMemoryCommitStore) extends Co
   }
 }
 
+/**
+ * A helper class which enables managed-commit for the test suite based on the given
+ * `managedCommitBackfillBatchSize` conf.
+ */
 trait ManagedCommitBaseSuite extends SparkFunSuite with SharedSparkSession {
-  val managedCommitBackfillBatchSize: Option[Int] = None
+
+  // If this config is not overridden, managed commits are disabled.
+  def managedCommitBackfillBatchSize: Option[Int] = None
+
+  final def managedCommitsEnabledInTests: Boolean = managedCommitBackfillBatchSize.nonEmpty
 
   override protected def sparkConf: SparkConf = {
-    var sparkConf = super.sparkConf
     if (managedCommitBackfillBatchSize.nonEmpty) {
       val managedCommitOwnerConf = Map("randomConf" -> "randomConfValue")
       val managedCommitOwnerJson = JsonUtils.toJson(managedCommitOwnerConf)
-      sparkConf = sparkConf
-        .set(DeltaConfigs.MANAGED_COMMIT_OWNER_NAME.defaultTablePropertyKey, "in-memory")
-        .set(
-          DeltaConfigs.MANAGED_COMMIT_OWNER_CONF.defaultTablePropertyKey,
-          managedCommitOwnerJson)
+      super.sparkConf
+        .set(DeltaConfigs.MANAGED_COMMIT_OWNER_NAME.defaultTablePropertyKey, "tracking-in-memory")
+        .set(DeltaConfigs.MANAGED_COMMIT_OWNER_CONF.defaultTablePropertyKey, managedCommitOwnerJson)
+    } else {
+      super.sparkConf
     }
-    sparkConf
   }
 
   override def beforeEach(): Unit = {
     super.beforeEach()
     CommitStoreProvider.clearNonDefaultBuilders()
     managedCommitBackfillBatchSize.foreach { batchSize =>
-      CommitStoreProvider.registerBuilder(InMemoryCommitStoreBuilder(batchSize))
+      CommitStoreProvider.registerBuilder(TrackingInMemoryCommitStoreBuilder(batchSize))
     }
   }
 }