[SPARK-28996][SQL][TESTS] Add tests regarding username of HiveClient

### What changes were proposed in this pull request?

This patch proposes to add new tests to test the username of HiveClient to prevent changing the semantic unintentionally. The owner of Hive table has been changed back-and-forth, principal -> username -> principal, and looks like the change is not intentional. (Please refer [SPARK-28996](https://issues.apache.org/jira/browse/SPARK-28996) for more details.) This patch intends to prevent this.

This patch also renames previous HiveClientSuite(s) to HivePartitionFilteringSuite(s) as it was commented as TODO, as well as previous tests are too narrowed to test only partition filtering.

### Does this PR introduce any user-facing change?

No.

### How was this patch tested?

Newly added UTs.

Closes #25696 from HeartSaVioR/SPARK-28996.

Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: HeartSaVioR

sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClient.scala

@@ -292,4 +292,6 @@ private[hive] trait HiveClient {
   /** Used for testing only.  Removes all metadata from this instance of Hive. */
   def reset(): Unit
 
+  /** Returns the user name which is used as owner for Hive table. */
+  def userName: String
 }

sql/hive/src/main/scala/org/apache/spark/sql/hive/client/HiveClientImpl.scala

@@ -222,7 +222,7 @@ private[hive] class HiveClientImpl(
     hiveConf
   }
 
-  private val userName = UserGroupInformation.getCurrentUser.getShortUserName
+  override val userName = UserGroupInformation.getCurrentUser.getShortUserName
 
   override def getConf(key: String, defaultValue: String): String = {
     conf.get(key, defaultValue)

sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientUserNameSuite.scala

@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.hive.client
+
+import java.security.PrivilegedExceptionAction
+
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.security.UserGroupInformation
+import org.scalatest.{BeforeAndAfterAll, PrivateMethodTester}
+
+import org.apache.spark.util.Utils
+
+class HiveClientUserNameSuite(version: String) extends HiveVersionSuite(version) {
+
+  test("username of HiveClient - no UGI") {
+    // Assuming we're not faking System username
+    assert(getUserNameFromHiveClient === System.getProperty("user.name"))
+  }
+
+  test("username of HiveClient - UGI") {
+    val ugi = UserGroupInformation.createUserForTesting(
+      "fakeprincipal@EXAMPLE.COM", Array.empty)
+    ugi.doAs(new PrivilegedExceptionAction[Unit]() {
+      override def run(): Unit = {
+        assert(getUserNameFromHiveClient === ugi.getShortUserName)
+      }
+    })
+  }
+
+  test("username of HiveClient - Proxy user") {
+    val ugi = UserGroupInformation.createUserForTesting(
+      "fakeprincipal@EXAMPLE.COM", Array.empty)
+    val proxyUgi = UserGroupInformation.createProxyUserForTesting(
+      "proxyprincipal@EXAMPLE.COM", ugi, Array.empty)
+    proxyUgi.doAs(new PrivilegedExceptionAction[Unit]() {
+      override def run(): Unit = {
+        assert(getUserNameFromHiveClient === proxyUgi.getShortUserName)
+      }
+    })
+  }
+
+  private def getUserNameFromHiveClient: String = {
+    val hadoopConf = new Configuration()
+    hadoopConf.set("hive.metastore.warehouse.dir", Utils.createTempDir().toURI().toString())
+    val client = buildClient(hadoopConf)
+    client.userName
+  }
+}

sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientUserNameSuites.scala

@@ -0,0 +1,28 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.hive.client
+
+import scala.collection.immutable.IndexedSeq
+
+import org.scalatest.Suite
+
+class HiveClientUserNameSuites extends Suite with HiveClientVersions {
+  override def nestedSuites: IndexedSeq[Suite] = {
+    versions.map(new HiveClientUserNameSuite(_))
+  }
+}

sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuite.scala renamed to sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HivePartitionFilteringSuite.scala

@@ -31,8 +31,7 @@ import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.types.{BooleanType, IntegerType, LongType, StructType}
 import org.apache.spark.util.Utils
 
-// TODO: Refactor this to `HivePartitionFilteringSuite`
-class HiveClientSuite(version: String)
+class HivePartitionFilteringSuite(version: String)
     extends HiveVersionSuite(version) with BeforeAndAfterAll {
 
   private val tryDirectSqlKey = HiveConf.ConfVars.METASTORE_TRY_DIRECT_SQL.varname

sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HiveClientSuites.scala renamed to sql/hive/src/test/scala/org/apache/spark/sql/hive/client/HivePartitionFilteringSuites.scala

@@ -21,9 +21,9 @@ import scala.collection.immutable.IndexedSeq
 
 import org.scalatest.Suite
 
-class HiveClientSuites extends Suite with HiveClientVersions {
+class HivePartitionFilteringSuites extends Suite with HiveClientVersions {
   override def nestedSuites: IndexedSeq[Suite] = {
     // Hive 0.12 does not provide the partition filtering API we call
-    versions.filterNot(_ == "0.12").map(new HiveClientSuite(_))
+    versions.filterNot(_ == "0.12").map(new HivePartitionFilteringSuite(_))
   }
 }