MAPREDUCE-7520 testCombineFileInputFormat is overly constrained and can sometimes fail

[18chanp1]

Description of PR

MAPREDUCE-7520

The Hadoop documentation states that the number of paths per split in CombineFileInputFormat is not fixed and can vary.

"If a maxSplitSize is specified, then blocks on the same node are combined to form a single split. Blocks that are left over are then combined with other blocks in the same rack." [hadoop.apache.org](https://hadoop.apache.org/docs/stable/api/org/apache/hadoop/mapred/lib/CombineFileInputFormat.html?utm_source=chatgpt.com)

This means that the number of paths in a split is determined by the block placement and the configuration settings, leading to potential variations in the number of paths per split.

This causes the test to sometimes fail depending on the split. As such, the test could be reworked to avoid strictly testing for the number of paths in each split.

This patch relaxes the assumptions by removing checks on number of paths per split and order per split (not guaranteed anywhere), focusing on whether the files exist

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?
• [X ] If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	8m 21s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		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	137m 21s	/branch-mvninstall-root.txt	root in trunk failed.
+1 💚	compile	0m 19s		trunk passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	compile	0m 19s		trunk passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	checkstyle	0m 18s		trunk passed
+1 💚	mvnsite	0m 24s		trunk passed
+1 💚	javadoc	0m 21s		trunk passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javadoc	0m 15s		trunk passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	spotbugs	0m 31s		trunk passed
+1 💚	shadedclient	19m 53s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 16s		the patch passed
+1 💚	compile	0m 16s		the patch passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javac	0m 16s		the patch passed
+1 💚	compile	0m 16s		the patch passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	javac	0m 16s		the patch passed
-1 ❌	blanks	0m 0s	/blanks-eol.txt	The patch has 3 line(s) that end in blanks. Use git apply --whitespace=fix <<patch_file>>. Refer https://git-scm.com/docs/git-apply
-0 ⚠️	checkstyle	0m 13s	/results-checkstyle-hadoop-mapreduce-project_hadoop-mapreduce-client_hadoop-mapreduce-client-jobclient.txt	hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient: The patch generated 4 new + 58 unchanged - 0 fixed = 62 total (was 58)
+1 💚	mvnsite	0m 18s		the patch passed
+1 💚	javadoc	0m 12s		the patch passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javadoc	0m 14s		the patch passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	spotbugs	0m 33s		the patch passed
+1 💚	shadedclient	20m 19s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	90m 8s	/patch-unit-hadoop-mapreduce-project_hadoop-mapreduce-client_hadoop-mapreduce-client-jobclient.txt	hadoop-mapreduce-client-jobclient in the patch passed.
+1 💚	asflicense	0m 26s		The patch does not generate ASF License warnings.
		282m 25s

Reason	Tests
Failed junit tests	hadoop.mapreduce.v2.TestUberAM

Subsystem	Report/Notes
Docker	ClientAPI=1.51 ServerAPI=1.51 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8010/1/artifact/out/Dockerfile
GITHUB PR	#8010
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 6255921d230c 5.15.0-153-generic #163-Ubuntu SMP Thu Aug 7 16:37:18 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / ddbfe1a
Default Java	Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8010/1/testReport/
Max. process+thread count	1222 (vs. ulimit of 5500)
modules	C: hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient U: hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8010/1/console
versions	git=2.25.1 maven=3.9.11 spotbugs=4.2.2
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