improve test style and assert

Author: dengziming

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDownSuite.scala

@@ -23,14 +23,21 @@ import org.apache.spark.sql.connector.read.SupportsPushDownJoin.ColumnWithAlias
 class V2ScanRelationPushDownSuite extends SparkFunSuite {
 
   private def assertAliases(
-                             leftInput: Array[String],
-                             rightInput: Array[String],
-                             expectedLeft: Array[ColumnWithAlias],
-                             expectedRight: Array[ColumnWithAlias]
-                           ): Unit = {
+    leftInput: Array[String],
+    rightInput: Array[String],
+    expectedLeft: Array[ColumnWithAlias],
+    expectedRight: Array[ColumnWithAlias]
+  ): Unit = {
     val (actualLeft, actualRight) = V2ScanRelationPushDown
       .generateColumnAliasesForDuplicatedName(leftInput, rightInput)
 
+    val uniqName : ColumnWithAlias => String = col => {
+      if (col.alias() == null) col.colName() else col.alias().toLowerCase()
+    }
+    // Ensure no duplicate column names after ignoring capitalization
+    assert((actualLeft++actualRight).map(uniqName).distinct.length
+      == actualLeft.length + actualRight.length)
+
     assert(
       actualLeft === expectedLeft,
       s"""Left side aliases mismatch.