add test

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/OptimizerSuite.scala

@@ -313,4 +313,41 @@ class OptimizerSuite extends PlanTest {
       assert(message1.contains("not a valid aggregate expression"))
     }
   }
+
+  test("validate schema output respects spark.sql.caseSensitive flag") {
+    /**
+     * A dummy optimizer rule for capitalizing alias.
+     */
+    object CapitalizeAttribute extends Rule[LogicalPlan] {
+      def apply(plan: LogicalPlan): LogicalPlan = plan transformExpressions {
+        case a: Alias =>
+          // scalastyle:off caselocale
+          Alias(a.child, a.name.toUpperCase)(a.exprId, a.qualifier, a.explicitMetadata)
+        // scalastyle:on caselocale
+      }
+    }
+
+    val optimizer = new SimpleTestOptimizer() {
+      override def defaultBatches: Seq[Batch] =
+        Batch("test", FixedPoint(1), CapitalizeAttribute) :: Nil
+    }
+
+    val query = Project(Alias(Literal(1), "attr")() :: Nil, OneRowRelation()).analyze
+
+    withSQLConf(SQLConf.CASE_SENSITIVE.key -> "false") {
+      try {
+        optimizer.execute(query)
+      } catch {
+        case sx: SparkException =>
+          fail("Query should run successfully with case insensitive setting.")
+      }
+    }
+
+    withSQLConf(SQLConf.CASE_SENSITIVE.key -> "true") {
+      val message = intercept[SparkException] {
+        optimizer.execute(query)
+      }.getMessage
+      assert(message.contains("The plan output schema has changed"))
+    }
+  }
 }