Remove thread pool in IT

Signed-off-by: Chen Dai <daichen@amazon.com>

Author: dai-chen

integ-test/src/test/scala/org/opensearch/flint/spark/FlintSparkIndexSqlITSuite.scala

@@ -5,10 +5,7 @@
 
 package org.opensearch.flint.spark
 
-import java.util.concurrent.Executors
-
 import scala.collection.JavaConverters._
-import scala.concurrent.{ExecutionContext, Future}
 
 import org.opensearch.action.admin.indices.settings.put.UpdateSettingsRequest
 import org.opensearch.client.RequestOptions
@@ -21,7 +18,6 @@ import org.opensearch.flint.spark.skipping.FlintSparkSkippingIndex
 import org.scalatest.matchers.should.Matchers
 
 import org.apache.spark.sql.Row
-import org.apache.spark.sql.functions.col
 
 class FlintSparkIndexSqlITSuite extends FlintSparkSuite with Matchers {
 
@@ -38,13 +34,6 @@ class FlintSparkIndexSqlITSuite extends FlintSparkSuite with Matchers {
   private val testMvIndex = s"spark_catalog.default.$testMvIndexShortName"
   private val testMvFlintIndex = FlintSparkMaterializedView.getFlintIndexName(testMvIndex)
 
-  /**
-   * Creates a custom `ExecutionContext` with a fixed thread pool for handling asynchronous
-   * operations in tests. TODO: move to base class if more tests require this.
-   */
-  implicit val executionContext: ExecutionContext =
-    ExecutionContext.fromExecutor(Executors.newFixedThreadPool(1))
-
   override def beforeAll(): Unit = {
     super.beforeAll()
     createTimeSeriesTable(testTableQualifiedName)
@@ -135,7 +124,7 @@ class FlintSparkIndexSqlITSuite extends FlintSparkSuite with Matchers {
     outputError shouldBe empty
 
     // Trigger next micro batch after 5 seconds with index readonly
-    Future {
+    new Thread(() => {
       Thread.sleep(5000)
       openSearchClient
         .indices()
@@ -145,7 +134,7 @@ class FlintSparkIndexSqlITSuite extends FlintSparkSuite with Matchers {
           RequestOptions.DEFAULT)
       sql(
         s"INSERT INTO $testTableQualifiedName VALUES (TIMESTAMP '2023-10-01 04:00:00', 'F', 25, 'Vancouver')")
-    }
+    }).start()
 
     // Await to store exception and verify if it's as expected
     flint.flintIndexMonitor.awaitMonitor(Some(testSkippingFlintIndex))