YARN-11899. TestRouterMetrics is order dependent

[18chanp1]

Description of PR

The following tests are order dependent if they are interleaved with some other tests.

org.apache.hadoop.yarn.server.router.TestRouterMetrics.testAppsFailedCreated
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testAppsFailedKilled
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testAppsFailedSubmitted
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testAppsReportFailed
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testMulipleAppsReportFailed
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testSucceededAppsCreated
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testSucceededAppsKilled
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testSucceededAppsReport
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testSucceededAppsSubmitted
org.apache.hadoop.yarn.server.router.TestRouterMetrics.testSucceededMultipleAppsReport

I believe this is because the Router is being used by some other module, causing the statistics to be inaccurate. To address this problem, RouterMetrics should be reset before and after every test. This PR creates a setup and teardown to perform this action

How was this patch tested?

Existing tests in TestRouterMetrics that pass continue to pass, and tests that fail in TestRouterMetrics continue to fail.

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	1m 12s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ trunk Compile Tests _
+1 💚	mvninstall	43m 47s		trunk passed
+1 💚	compile	0m 34s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	compile	0m 34s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	checkstyle	0m 29s		trunk passed
+1 💚	mvnsite	0m 39s		trunk passed
+1 💚	javadoc	0m 37s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javadoc	0m 33s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	spotbugs	1m 3s		trunk passed
+1 💚	shadedclient	31m 12s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 26s		the patch passed
+1 💚	compile	0m 26s		the patch passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javac	0m 26s		the patch passed
+1 💚	compile	0m 26s		the patch passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	javac	0m 26s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 18s		the patch passed
+1 💚	mvnsite	0m 29s		the patch passed
+1 💚	javadoc	0m 25s		the patch passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javadoc	0m 23s		the patch passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	spotbugs	1m 3s		the patch passed
+1 💚	shadedclient	30m 45s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	14m 52s	/patch-unit-hadoop-yarn-project_hadoop-yarn_hadoop-yarn-server_hadoop-yarn-server-router.txt	hadoop-yarn-server-router in the patch passed.
+1 💚	asflicense	0m 35s		The patch does not generate ASF License warnings.
		133m 1s

Reason	Tests
Failed junit tests	hadoop.yarn.server.router.webapp.TestFederationWebApp
	hadoop.yarn.server.router.subcluster.fair.TestYarnFederationWithFairScheduler

Subsystem	Report/Notes
Docker	ClientAPI=1.52 ServerAPI=1.52 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8133/1/artifact/out/Dockerfile
GITHUB PR	#8133
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux fc9a9ad51c75 5.15.0-160-generic #170-Ubuntu SMP Wed Oct 1 10:06:56 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / af0e230
Default Java	Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8133/1/testReport/
Max. process+thread count	1225 (vs. ulimit of 5500)
modules	C: hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router U: hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8133/1/console
versions	git=2.25.1 maven=3.9.11 spotbugs=4.9.7
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[ayushtkn]

isn't just doing in BeforeEach enough?