HDFS-9888. Allow reseting KerberosName in unit tests. Contributed by Xiao Chen.

(cherry picked from commit 3e8099a45a)
(cherry picked from commit 00ff3d737c)

hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/util/KerberosName.java

@@ -25,6 +25,7 @@ import java.util.Locale;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import com.google.common.annotations.VisibleForTesting;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.slf4j.Logger;
@@ -90,6 +91,16 @@ public class KerberosName {
     }
   }
 
+  @VisibleForTesting
+  public static void resetDefaultRealm() {
+    try {
+      defaultRealm = KerberosUtil.getDefaultRealm();
+    } catch (Exception ke) {
+      LOG.debug("resetting default realm failed, "
+          + "current default realm will still be used.", ke);
+    }
+  }
+
   /**
    * Create a name from the full Kerberos principal name.
    * @param name full Kerberos principal name.

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/balancer/TestBalancer.java

@@ -106,6 +106,7 @@ import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.LazyPersistTestCase
 import org.apache.hadoop.http.HttpConfig;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.minikdc.MiniKdc;
+import org.apache.hadoop.security.authentication.util.KerberosName;
 import org.apache.hadoop.security.SecurityUtil;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.security.ssl.KeyStoreTestUtil;
@@ -152,6 +153,7 @@ public class TestBalancer {
     SecurityUtil.setAuthenticationMethod(
         UserGroupInformation.AuthenticationMethod.KERBEROS, conf);
     UserGroupInformation.setConfiguration(conf);
+    KerberosName.resetDefaultRealm();
     assertTrue("Expected configuration to enable security",
         UserGroupInformation.isSecurityEnabled());
 
@@ -1854,10 +1856,10 @@ public class TestBalancer {
   @Test(timeout = 300000)
   public void testBalancerWithKeytabs() throws Exception {
     final Configuration conf = new HdfsConfiguration();
+    try {
       initSecureConf(conf);
       final UserGroupInformation ugi = UserGroupInformation.loginUserFromKeytabAndReturnUGI(
           principal, keytabFile.getAbsolutePath());
-    try {
       ugi.doAs(new PrivilegedExceptionAction<Void>() {
         @Override
         public Void run() throws Exception {