[FLINK-29775][tests][JUnit5 migration] Module: flink-statebackend-rocksdb

[spuru9]

What is the purpose of the change

Migrates the remaining JUnit 4 tests in flink-statebackend-rocksdb to JUnit 5 and converts their assertions to AssertJ, as part of FLINK-25325.

Most tests in this module have a near-identical sibling in flink-statebackend-forst, which was migrated in FLINK-39767 (6627acb). Where a sibling exists, this PR follows it so the two modules stay consistent.

After this change the module has no reference to org.junit.* (outside org.junit.jupiter), no Hamcrest matchers, and no TestLogger.

Brief change log

• @Rule / @ClassRule TemporaryFolder → @TempDir. A test that needs a single directory takes it as a method parameter (@TempDir File dir); TempDirUtils.newFolder(root) is kept only where one test needs several distinct directories.
• @RunWith(Parameterized.class) → @ExtendWith(ParameterizedTestExtension.class) + @TestTemplate in RocksIncrementalCheckpointRescalingTest, matching ForStIncrementalCheckpointRescalingTest.
• @Test(expected = ...) and the manual try { ...; fail(); } catch (X e) { ... } blocks → assertThatThrownBy(...) / assertThatCode(...).doesNotThrowAnyException().
• org.junit.Assert and Hamcrest matchers → AssertJ, preferring the native idioms (hasSize, containsExactly, containsExactlyInAnyOrderElementsOf, isInstanceOf, hasToString, hasBinaryContent, exists/doesNotExist, allMatch, satisfiesAnyOf, hasCause/hasMessageContaining).
• org.junit.Assume → org.junit.jupiter.api.Assumptions.
• Dropped extends TestLogger and the now-unnecessary public modifiers on test classes and methods.
• RocksDBExtension and RocksDBKeyedStateBackendTestFactory are test utilities rather than tests, but were still holding a JUnit 4 TemporaryFolder. RocksDBExtension (itself a JUnit 5 extension, so it cannot use @TempDir injection) now creates and deletes its own temp directory; RocksDBKeyedStateBackendTestFactory.create(...) takes a java.nio.file.Path instead.

Assertion messages were kept via .as(...). The ones that disappear are fail("...should have thrown")-style messages, which assertThatThrownBy expresses natively, and messages whose content AssertJ already prints (e.g. assertThat(errorRef.get()).isNull() prints the throwable).

Verifying this change

This change is a test-only rework; it is verified by the existing tests it migrates.

mvn verify -pl flink-state-backends/flink-statebackend-rocksdb passes with the same number of tests before and after, per class:

• before: 843 unit tests (9 skipped) + 2 integration tests
• after: 843 unit tests (9 skipped) + 2 integration tests

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code)

Generated-by: Claude Code (claude-opus-5)

[flinkbot]

CI report:

• 2468e39 Azure: SUCCESS

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[spuru9]

extends TestLoggeris dropped without adding aMETA-INF/servicesfile —TestLoggerExtensionis already auto-registered from theflink-streaming-java` test-jar this module depends on.