discussion: adding unit/integration tests for client . files

[kunstewi]

Proposed Tests

File	Type	What to Cover
i18n.js	Unit	languageKeyToLabel, languageKeyToDateLocale, currentDateLocale, language selection precedence (window.INITIAL_STATE vs detected fallback)
persistState.ts	Unit	Save/load/clear happy paths, invalid JSON, missing storage values, storage errors with console.warn
reducers.ts	Smoke?	Needs discussion — unsure if a smoke test is worth adding to verify combined state shape keys and init state, without re testing each child reducer deeply.
store.ts	Unit	showReduxDevTools() conditions, setupStore() behavior (persisted state precedence, clearState called, dev-tools enhancer toggling)
theme.js	Unit	remSize, prop success/error states, extend immutability/deep merge, key overrides in contrast theme

Files I'm skipping (browserHistory.js, constants.js, middleware.js) — don't seem to need tests, but open to feedback.

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Discussion Questions

1. Which files actually need tests? Are the files in the table above the right ones to focus on, or are some not worth testing? Should reducers.ts get a smoke test?

2. Is this a priority right now? If not, which folders/files in the codebase would benefit most from test coverage first?

3. Should we update testing.md? Currently it's hard to know which files need tests. Would it make sense to add a checklist of all files that need coverage to testing.md in the contributor docs, and check them off as coverage improves? This would make it easier for contributors to pick up testing tasks without guessing.