HDDS-7566. Refactor TestRocksDBCheckpointDiffer tests.

[jojochuang]

What changes were proposed in this pull request?

HDDS-7566. Refactor TestRocksDBCheckpointDiffer tests.

Please describe your PR in detail:

• The original issue meant to refactor the CompactionDag out of RocksDBCheckpointDiffer, which is already implemented. But the test is not.
• Therefore, moved CompactionDag specific tests from TestRocksDBCheckpointDiffer to a new TestCompactionDag class. This makes the tests more organized and easier to maintain.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-7566

How was this patch tested?

mvn test -Dtest=TestCompactionDag,TestRocksDBCheckpointDiffer

[jojochuang]

@smengcl @sadanand48 @SaketaChalamchala this is a trivial refactor.

[SaketaChalamchala]

Thanks for the patch @jojochuang . We can also move testPruneOlderSnapshotsWithCompactionHistory to the TestCompactionDag class as it tests removing nodes (SST files) from the DAG that are older than configured time.

[Copilot]

Pull Request Overview

This PR refactors test organization by moving CompactionDag-specific tests from TestRocksDBCheckpointDiffer to a new dedicated TestCompactionDag class, improving test maintainability and organization.

• Removes CompactionDag-related test constants, helper methods, and test cases from TestRocksDBCheckpointDiffer
• Creates new TestCompactionDag class with moved CompactionDag-specific tests
• Updates test methods to use CompactionDag instance instead of RocksDBCheckpointDiffer

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
TestRocksDBCheckpointDiffer.java	Removes CompactionDag-specific test constants, helper methods, and test cases
TestCompactionDag.java	New test class containing all moved CompactionDag-specific tests and utilities

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[Copilot]

Redundant variable assignment. The variable dag is already initialized on line 115 with the same value. Remove this duplicate assignment.

Suggested change

dag = GraphBuilder.directed().build();

[Copilot]

The comment incorrectly describes test cases for pruneBackwardDag when this method provides test cases for pruneForwardDag. Update the comment to 'Test cases for pruneForwardDag.'

Suggested change

	* Test cases for pruneBackwardDag.
	* Test cases for pruneForwardDag.

[smengcl]

Thanks @jojochuang . I don't have more to add except pls address @SaketaChalamchala 's comment above.

[jojochuang]

Merged with Saketa's suggestion. Thanks @smengcl @SaketaChalamchala