Reduce duplicate custom scalars tests between core APIs and React hooks

[jerelmiller]

When I first started working on custom scalars, I added tests all over the place to ensure it works throughout the entirety of the library. The problem however is that I essentially duplicated the entire test suite across every React hook. Since all React hooks use client.watchQuery under the hood, client.watchQuery tests really should be the test suite that checks all the edge cases (fetch policies, defer/stream, etc.), otherwise future maintenance is going to be a nightmare if we have to duplicate new tests for every React hooks.

The React hook custom scalars test suites are now reduced to a more minimal set to ensure the integration works as expected, but the core APIs are now where the full suite lives. This will make it easier to add tests in the future without having to duplicate them everywhere.

Summary by CodeRabbit

• Tests
  • Expanded coverage for custom scalar parsing, including Date values returned through deferred and incremental responses.
  • Updated query, mutation, subscription, suspense, and preloader scenarios to validate parsed scalar fields and variables.
  • Added checks that identical scalar results preserve stable data references and avoid unnecessary updates.
  • Refined error-policy and loading-state expectations for successful parsed results.

[apollo-librarian]

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Build ID: 068947bfeed68865c514b534
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ℹ️ Recent review info

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Review profile: CHILL

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Run ID: 982cf861-073a-4d39-bb88-54f55cddbf3a

📥 Commits

Reviewing files that changed from the base of the PR and between 7aaa484 and 421541d.

📒 Files selected for processing (10)

• src/core/__tests__/client.mutate/customScalars.test.ts
• src/react/hooks/__tests__/useBackgroundQuery/customScalars.test.tsx
• src/react/hooks/__tests__/useLazyQuery/customScalars.test.tsx
• src/react/hooks/__tests__/useLoadableQuery/customScalars.test.tsx
• src/react/hooks/__tests__/useMutation/customScalars.test.tsx
• src/react/hooks/__tests__/useQuery/customScalars.test.tsx
• src/react/hooks/__tests__/useQueryRefHandlers/customScalars.test.tsx
• src/react/hooks/__tests__/useSubscription/customScalars.test.tsx
• src/react/hooks/__tests__/useSuspenseQuery/customScalars.test.tsx
• src/react/query-preloader/__tests__/createQueryPreloader/customScalars.test.tsx

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📝 Walkthrough

Walkthrough

Custom scalar tests now emphasize parsed Date fields, referential identity across refetches and subscriptions, successful query-preloader states, and mutation parsing across two @defer payload formats. Older incremental, error-policy, optimistic, and updater scenarios were removed.

Changes

Custom scalar coverage

Layer / File(s)	Summary
Deferred mutation scalar parsing src/core/__tests__/client.mutate/customScalars.test.ts	Adds coverage for parsing Date values across deferred mutation chunks using both incremental handlers.
React hook scalar parsing and identity src/react/hooks/__tests__/useBackgroundQuery/*, src/react/hooks/__tests__/useLoadableQuery/*, src/react/hooks/__tests__/useQuery/*, src/react/hooks/__tests__/useSubscription/*, src/react/hooks/__tests__/useSuspenseQuery/*, src/react/hooks/__tests__/useQueryRefHandlers/*	Refocuses hook tests on parsed scalar fields and referential identity, while removing older incremental and error-policy scenarios.
Lazy query and mutation expectations src/react/hooks/__tests__/useLazyQuery/customScalars.test.tsx, src/react/hooks/__tests__/useMutation/customScalars.test.tsx	Updates parsed variable and field assertions, successful error-policy snapshots, and stable data checks; removes superseded mutation scenarios.
Query preloader scalar state src/react/query-preloader/__tests__/createQueryPreloader/customScalars.test.tsx	Validates parsed scalar output, ready states, and unchanged data references after a network-only query.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• apollographql/apollo-client#13252: Adds the custom-scalar cache plumbing exercised by these tests.
• apollographql/apollo-client#13270: Covers scalar coercion and incremental custom-scalar handling related to these assertions.
• apollographql/apollo-client#13319: Updates custom-scalar parsing coverage for incremental payloads.

Suggested labels: auto-cleanup

Suggested reviewers: phryneas, daleseo

Poem

I’m a bunny with Dates in my queue,
Deferred little chunks hop through too.
Hooks keep references tight,
Scalars parse just right—
And old test thickets bid adieu!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: consolidating duplicate custom scalar test coverage between core APIs and React hooks.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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src/core/__tests__/client.mutate/customScalars.test.ts

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src/react/hooks/__tests__/useBackgroundQuery/customScalars.test.tsx

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src/react/hooks/__tests__/useLazyQuery/customScalars.test.tsx

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[pkg-pr-new]

npm i https://pkg.pr.new/@apollo/client@13368

commit: 421541d