[A] Reason of failure:
Before executing the UT, there is already a file under the INPUT_DIR used as the MR input dir, such as 'hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/target/test-dir/input/0'. So the MR result is incorrect, as the input dir includes extra file.

[B] Solution:
Update UT code to remove the whole INPUT_DIR before execution, not only removing INPUT_FILE. (I did such tests and they all passed)

Remove the whole INPUT_DIR before runing MR job, not only remove the INPUT_FILE. This enhancement will also remove other unexpected files under INPUT_DIR.

Before running the UT, to remove the whole INPUT_DIR, not only the INPUT_FILE. This enhancement will clean other unexpected files under folder INPUT_DIR.

I ran some tests after applying this patch and they all passed.

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12686433/MAPREDUCE-6191.patch
against trunk revision 9a44db4.

+1 @author. The patch does not contain any @author tags.

+1 tests included. The patch appears to include 1 new or modified test files.

+1 javac. The applied patch does not increase the total number of javac compiler warnings.

+1 javadoc. There were no new javadoc warning messages.

+1 eclipse:eclipse. The patch built with eclipse:eclipse.

+1 findbugs. The patch does not introduce any new Findbugs (version 2.0.3) warnings.

+1 release audit. The applied patch does not increase the total number of release audit warnings.

-1 core tests. The following test timeouts occurred in hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient:

org.apache.hadoop.mapreduce.lib.output.TestJobOutputCommitter

Test results: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5072//testReport/
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5072//console

This message is automatically generated.

In the latest test result, this UT passed and the patch works well.
Running org.apache.hadoop.mapred.TestJavaSerialization
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 4.204 sec - in org.apache.hadoop.mapred.TestJavaSerialization

https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5072//consoleFull

+1 looks good.

I just committed this, thanks Sam.

FAILURE: Integrated in Hadoop-trunk-Commit #6727 (See https://builds.apache.org/job/Hadoop-trunk-Commit/6727/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/CHANGES.txt
• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java

FAILURE: Integrated in Hadoop-Yarn-trunk-Java8 #43 (See https://builds.apache.org/job/Hadoop-Yarn-trunk-Java8/43/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/CHANGES.txt
• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java

FAILURE: Integrated in Hadoop-Yarn-trunk #777 (See https://builds.apache.org/job/Hadoop-Yarn-trunk/777/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/CHANGES.txt
• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java

FAILURE: Integrated in Hadoop-Mapreduce-trunk #1994 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk/1994/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/CHANGES.txt
• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java

FAILURE: Integrated in Hadoop-Hdfs-trunk #1975 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk/1975/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java
• hadoop-mapreduce-project/CHANGES.txt

FAILURE: Integrated in Hadoop-Hdfs-trunk-Java8 #40 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk-Java8/40/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java
• hadoop-mapreduce-project/CHANGES.txt

FAILURE: Integrated in Hadoop-Mapreduce-trunk-Java8 #44 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk-Java8/44/)
MAPREDUCE-6191. Improve clearing stale state of Java serialization (eyang: rev c379e102ddab1b83fd69e4492a40c9901fb50675)

• hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/mapred/TestJavaSerialization.java
• hadoop-mapreduce-project/CHANGES.txt

Jenkins failure is not related to this commit. There are changes since December 12 which is breaking trunk:

HADOOP-11353. Add support for .hadooprc (aw) (detail)
YARN-2917. Fixed potential deadlock when system.exit is called in AsyncDispatcher. Contributed by Rohith Sharmaks (detail)
HDFS-7515. Fix new findbugs warnings in hadoop-hdfs. Contributed by Haohui Mai. (detail)
HADOOP-11211. mapreduce.job.classloader.system.classes semantics should be order-independent. (Yitong Zhou via gera) (detail)
HDFS-7449. Add metrics to NFS gateway. Contributed by Brandon Li (detail)
HADOOP-11389. Clean up byte to string encoding issues in hadoop-common. Contributed by Haohui Mai. (detail)
HDFS-7497. Inconsistent report of decommissioning DataNodes between dfsadmin and NameNode webui. Contributed by Yongjun Zhang. (detail)
MAPREDUCE-6046. Change the class name for logs in RMCommunicator. (detail)
YARN-2243. Order of arguments for Preconditions.checkNotNull() is wrong in (detail)

I committed this to branch-2, branch-2.8, branch-2.7, and branch-2.6.

FAILURE: Integrated in Hadoop-trunk-Commit #9274 (See https://builds.apache.org/job/Hadoop-trunk-Commit/9274/)
Update CHANGES.txt for commit of MAPREDUCE-6191 to other branches. (jlowe: rev a429f857b2aea63e23128728274bb2985c5bf087)

• hadoop-mapreduce-project/CHANGES.txt

Closing the JIRA as part of 2.7.3 release.