maven surefire-plugin is skipping tests - junit4

Question

Recently in our hadoop project, we added maven-surefire-plugin for running unit tests by categories. Related blocks in hadoop root pom.xml file as below:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.21.0</version>
<configuration>
<groups>${test.groups}</groups>
</configuration>
<dependencies>
<dependency>
<groupId>org.apache.maven.surefire</groupId>
<artifactId>surefire-junit47</artifactId>
<version>2.21.0</version>
</dependency>
</dependencies>
</plugin>
<profile>
<id>flakies</id>
<properties>
<test.groups>org.apache.hadoop.classification.TestJUnitCategory$FlakiesTest</test.groups>
</properties>
</profile>
<profile>
<id>stables</id>
<properties>
<test.groups>org.apache.hadoop.classification.TestJUnitCategory$StablesTest</test.groups>
</properties>
</profile>
<profile>
<id>integrations</id>
<properties>
<test.groups>org.apache.hadoop.classification.TestJUnitCategory$IntegrationsTest</test.groups>
</properties>
</profile>
<profile>
<id>none</id>
<properties>
<test.groups>!org.apache.hadoop.classification.TestJUnitCategory$AllTest</test.groups>
</properties>
</profile>
Invoking tests by category works fine: mvn -P integrations.
However, our old fashioned unit test execution got skipped by this maven-surefire-plugin:
13:16:35 [INFO] --- maven-antrun-plugin:1.7:run (create-log-dir) # hadoop-hdfs ---
13:16:35 [INFO] Executing tasks
13:16:35
13:16:35 main:
13:16:35 [delete] Deleting directory /tmp/tmp.o7flMN8505/src/ghuang/ghuang/hadoop-hdfs-project/hadoop-hdfs/target/test/data
13:16:35 [mkdir] Created dir: /tmp/tmp.o7flMN8505/src/ghuang/ghuang/hadoop-hdfs-project/hadoop-hdfs/target/test/data
13:16:35 [copy] Copying 16 files to /tmp/tmp.o7flMN8505/src/ghuang/ghuang/hadoop-hdfs-project/hadoop-hdfs/target/test-classes/webapps
13:16:35 [INFO] Executed tasks
13:16:35 [INFO]
13:16:35 [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) # hadoop-hdfs ---
13:16:35 [INFO] Nothing to compile - all classes are up to date
13:16:35 [INFO]
13:16:35 [INFO] --- maven-surefire-plugin:2.20:test (default-test) # hadoop-hdfs ---
13:16:35 [INFO] Surefire report directory: /tmp/tmp.o7flMN8505/src/ghuang/ghuang/hadoop-hdfs-project/hadoop-hdfs/target/surefire-reports
13:16:35 [INFO] parallel='none', perCoreThreadCount=true, threadCount=0, useUnlimitedThreads=false, threadCountSuites=0, threadCountClasses=0, threadCountMethods=0, parallelOptimized=true
13:16:35 [INFO]
13:16:35 [INFO] -------------------------------------------------------
13:16:35 [INFO] T E S T S
13:16:35 [INFO] -------------------------------------------------------
13:26:01 [INFO]
13:26:01 [INFO] Results:
13:26:01 [INFO]
13:26:01 [INFO] Tests run: 0, Failures: 0, Errors: 0, Skipped: 0
13:26:01 [INFO]
13:26:01 [INFO]
13:26:01 [INFO] --- maven-antrun-plugin:1.7:run (hdfs-test-bats-driver) # hadoop-hdfs ---
I also verified that by removing surefire-plugin block in root pom.xml file will make these tests executing again as usual. So I have some questions here:
Why tests were skipped in this case?
I saw the reported surefire-plugin version was 2.20 while I was defining 2.21 in my change. I assume this is because it gets overwritten by the parent pom. So how do I make it use my customized version?
Is the version 2.21 the right version for this? I saw some post indicated version 2.21 might have some bug?
Many thanks,