[SPARK-20156][SQL][FOLLOW-UP] Java String toLowerCase "Turkish locale bug" in Database and Table DDLs

### What changes were proposed in this pull request?
Database and Table names conform the Hive standard ("[a-zA-z_0-9]+"), i.e. if this name only contains characters, numbers, and _.

When calling `toLowerCase` on the names, we should add `Locale.ROOT` to the `toLowerCase`for avoiding inadvertent locale-sensitive variation in behavior (aka the "Turkish locale problem").

### How was this patch tested?
Added a test case

Author: Xiao Li <gatorsmile@gmail.com>

Closes #17655 from gatorsmile/locale.

1 files changed, 27 insertions, 1 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala b/sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala
index 6a4cc95d36..b5ad73b746 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/test/SQLTestUtils.scala
@@ -20,7 +20,7 @@ package org.apache.spark.sql.test
 import java.io.File
 import java.net.URI
 import java.nio.file.Files
-import java.util.UUID
+import java.util.{Locale, UUID}
 
 import scala.language.implicitConversions
 import scala.util.control.NonFatal
@@ -229,6 +229,32 @@ private[sql] trait SQLTestUtils
   }
 
   /**
+   * Drops database `dbName` after calling `f`.
+   */
+  protected def withDatabase(dbNames: String*)(f: => Unit): Unit = {
+    try f finally {
+      dbNames.foreach { name =>
+        spark.sql(s"DROP DATABASE IF EXISTS $name")
+      }
+    }
+  }
+
+  /**
+   * Enables Locale `language` before executing `f`, then switches back to the default locale of JVM
+   * after `f` returns.
+   */
+  protected def withLocale(language: String)(f: => Unit): Unit = {
+    val originalLocale = Locale.getDefault
+    try {
+      // Add Locale setting
+      Locale.setDefault(new Locale(language))
+      f
+    } finally {
+      Locale.setDefault(originalLocale)
+    }
+  }
+
+  /**
    * Activates database `db` before executing `f`, then switches back to `default` database after
    * `f` returns.
    */