[OPIK-8181] [BE] refactor: centralise dataset item test assertions in DatasetItemAssertions

[JetoPistola]

Details

IGNORED_FIELDS_DATA_ITEM was declared twice — once in DatasetsResourceTest and again, independently, in ExperimentAggregatesIntegrationTest — while DatasetVersionResourceTest imported it across package boundaries from a sibling test class. Thirteen call sites then re-derived the same usingRecursiveFieldByFieldElementComparatorIgnoringFields(...) chain by hand. This introduces a DatasetItemAssertions helper under api/resources/utils/datasets/ that owns the constant and the assertion methods, following the existing TraceAssertions shape, and migrates every call site onto it.

• The two declarations had already drifted. The ExperimentAggregatesIntegrationTest copy was missing runSummariesByExperiment, a later-added derived field it never picked up. Reconciled on the union (9 fields): both files compare DatasetItems returned by the same endpoints, so the omission was staleness rather than a legitimate difference. Verified by a full green run of that suite (145/145) — the wider ignore set does not mask any assertion there.
• Five methods rather than one. Call sites use genuinely different terminators (isEqualTo, containsExactlyElementsOf, containsExactlyInAnyOrder, containsAll, single-item recursive), so one signature could not cover them without contorting callers. The constant stays public on the helper for the few bespoke chains — exactly what TraceAssertions does — which satisfies single-ownership without forcing every site through a method.
• ignoredFieldsPlus("data") replaces a mutable ArrayList copy at the one call site that ignores an extra field and then asserts it separately, reusing the Stream.concat idiom already established in ExperimentTestAssertions.
• Standardised the helper on (actual, expected) argument order — the dominant convention and AssertJ's own reading order. Two of the former local helpers took (expected, actual).
• .agents/skills/opik-backend/testing.md now leads with helper-over-constant reuse and names the six helpers that exist, so the next author reaches for the helper instead of copying a comparator chain.

Test-only change: no production code. Assertion semantics are unchanged at every call site bar one, called out below.

Review follow-up — one place the union reconciliation did change coverage. Routing ExperimentAggregatesIntegrationTest through the shared helper newly ignored runSummariesByExperiment, which its local constant had not ignored on main. The two lists differed there for a reason: ExperimentAggregatesDAO's parity query omits assertions_array (the mapper guards this with size() > ASSERTIONS_INDEX and degrades to null), while DatasetItemVersionDAO includes it — so this is precisely the field that parity test exists to compare. assertDatasetItemsWithExperimentItems now asserts it explicitly alongside the existing experiment-items loop, restoring the coverage while keeping the shared helper. No fixture exercises it today (none create suite_assertion scores), so nothing was masked — the loss was future protection. Raised by the automated reviewer; the accompanying suggestion to add assertions_array to the production DAO query is deliberately out of scope for a test-only ticket.

Change checklist

• User facing
• Documentation update

Issues

• OPIK-8181

AI-WATERMARK

AI-WATERMARK: yes

• Tools: Claude Code
• Model(s): Claude Opus 5
• Scope: full implementation
• Human verification: pending author review

Testing

Commands run (from apps/opik-backend):

• mvn test -Dtest='ExperimentAggregatesIntegrationTest' — 145/145 pass, BUILD SUCCESS, re-run after adding the explicit runSummariesByExperiment parity assertion described above. This is the suite where the change is semantically meaningful.
• mvn test -Dtest='DatasetsResourceTest,DatasetVersionResourceTest,ExperimentAggregatesIntegrationTest' — every migrated call site's class passes: all 21 DatasetVersionResourceTest nested classes (9 migrations), and the dataset-item classes in DatasetsResourceTest (4 migrations) at 163/163 — CreateDatasetItems, GetDatasetItem, GetDatasetItemsByDatasetId, DeleteDatasetItems, FindDatasetItemsWithExperimentItems, FindDatasetItemsWithExperimentItemsSortingTest, FindDatasetItemsWithExperimentItemsAssertionResults.
• mvn compile -DskipTests — clean.
• mvn spotless:check — clean.

Environment: local, Testcontainers (MySQL + ClickHouse + Redis + ZooKeeper), macOS.

Tests not passing locally, with reason: the dataset-level classes in DatasetsResourceTest (FindDatasets, CreateDataset, GetDataset, ApiKey, SessionTokenCookie, ExperimentSummaryEnrichment) fail with HTTP 500 in this environment. These are pre-existing and unrelated — confirmed by running DatasetsResourceTest$FindDatasets against an unmodified origin/main checkout, which fails 37/74 identically (same tests, same line, same 500). None of those classes are touched by this PR, and a test-only assertion refactor cannot produce server-side 500s. Relying on CI for a clean environment run of those classes.

Documentation

.agents/skills/opik-backend/testing.md — the partial-comparison guidance now states that an existing assertion helper method or class takes precedence over inlining a shared ignore-field constant, names the six helpers under api/resources/utils/, documents ignoredFieldsPlus for the extra-field case, and says to add a new helper rather than hoist a constant into a test class when more than one class needs the assertion. The hasSize example in the same section was updated to call the helper instead of showing a raw comparator chain.

Revised after review feedback: the one-declaration rule is now scoped to the comparisons a helper actually covers, and explicitly permits a call site whose contract genuinely differs to ignore a different set — provided it derives from the shared constant via ignoredFieldsPlus rather than rebuilding the list. DatasetsResourceProjectScopedTest is the real case that motivated this: its expected item keeps id == null while the API generates one, so its ignore set legitimately includes id. The section also now warns about the trap this PR itself hit — a field one comparison ignores and another asserts is a real difference, not drift, and folding it into the shared list quietly drops coverage.

[github-actions]

⏱️ pre-commit per-hook timing

Hook	Description	Result	Duration
☕ spotless — java backend	Format Java code	✅	5.06s
Total (1 ran)			5.06s

⏭️ 43 skipped (no matching files changed)

Hook	Description	Result
🐍 trim trailing whitespace — python sdk	Strip trailing whitespace	⏭️
🐍 fix end of files — python sdk	Ensure files end in a newline	⏭️
🐍 ruff — python sdk	Lint + autofix Python (ruff)	⏭️
🐍 ruff-format — python sdk	Format Python code (ruff)	⏭️
🐍 mypy — python sdk	Static type check	⏭️
🤖 trim trailing whitespace — optimizer	Strip trailing whitespace	⏭️
🤖 fix end of files — optimizer	Ensure files end in a newline	⏭️
🤖 check yaml — optimizer	Validate YAML syntax	⏭️
🤖 check json — optimizer	Validate JSON syntax	⏭️
🤖 check toml — optimizer	Validate TOML syntax	⏭️
🤖 check for added large files — optimizer	Block large files (>1MB)	⏭️
🔐 detect private key — optimizer	Block committed private keys	⏭️
🤖 check for merge conflicts — optimizer	Block merge-conflict markers	⏭️
🤖 check for case conflicts — optimizer	Block case-only name clashes	⏭️
🤖 pyupgrade — optimizer	Modernize Python syntax	⏭️
🤖 ruff — optimizer	Lint + autofix Python (ruff)	⏭️
🤖 ruff-format — optimizer	Format Python code (ruff)	⏭️
🤖 mypy — optimizer	Static type check	⏭️
📓 nbstripout — optimizer notebooks	Strip notebook output	⏭️
📝 markdownlint — optimizer	Lint Markdown	⏭️
🔤 codespell — optimizer	Fix common misspellings	⏭️
📊 radon cc — optimizer	Cyclomatic-complexity gate	⏭️
📊 radon raw — optimizer	Raw size metrics gate	⏭️
📊 xenon — optimizer	Fail on complexity thresholds	⏭️
📊 lizard — optimizer	Cyclomatic-complexity gate	⏭️
🧹 vulture — optimizer	Find dead code	⏭️
🛡️ trim trailing whitespace — guardrails	Strip trailing whitespace	⏭️
🛡️ fix end of files — guardrails	Ensure files end in a newline	⏭️
🛡️ ruff — guardrails	Lint + autofix Python (ruff)	⏭️
🛡️ ruff-format — guardrails	Format Python code (ruff)	⏭️
🛡️ mypy — guardrails	Static type check	⏭️
⚓ helm-docs	Regenerate Helm chart README	⏭️
block non-public FE plugins	Block non-public FE plugins	⏭️
🧪 pre-commit wrapper smoke tests	Self-test the wrapper scripts	⏭️
🧪 rebaseline script tests	Self-test the changelog re-baseline script	⏭️
🌐 eslint — frontend	Lint + autofix JS/TS	⏭️
🌐 typecheck — frontend	Whole-project tsc type check	⏭️
📘 eslint — typescript sdk	Lint + autofix JS/TS	⏭️
📘 typecheck — typescript sdk	Whole-project tsc type check	⏭️
⚙️ actionlint — github workflows	Lint GitHub Actions workflows	⏭️
🐳 hadolint — dockerfiles	Lint Dockerfiles	⏭️
🌈 zizmor — github workflows security	Security-scan GitHub Actions workflows	⏭️
🛡️ semgrep — java backend sql	Block SQL injection-prone string formatting	⏭️

[CometActions]

No test needed here.

Test-only refactor: all four Java files are under src/test/java (the new DatasetItemAssertions helper plus its three call sites), and the fifth changed file is .agents/skills/opik-backend/testing.md. No production code changed, so there is no user- or API-visible behaviour for an e2e test to cover. Worth noting the one real behaviour change is inside the tests themselves: the shared IGNORED_FIELDS_DATA_ITEM adds runSummariesByExperiment, which ExperimentAggregatesIntegrationTest previously compared — you already re-assert it explicitly there, so the parity check is preserved.

Run

Advisory, from the QA test radar. Nothing here blocks this PR, and anything it proposes is a draft for review.

[andrescrz]

LGTM