test: improve unit test coverage with 16 new test files

[devin-ai-integration]

test: add 16 new unit test files for reducers, selectors, and utils

Summary

Adds unit tests for 16 previously untested files across reducers, selectors, utilities, and core constants. All tests follow existing patterns in the codebase.

Reducers (8 files):

• alert — SHOW_ALERT, HIDE_ALERT, initial state, unknown actions
• bookmarks — ADD_BOOKMARK, REMOVE_BOOKMARK, edge cases
• modals — all toggle actions including show: false, show: null, toggling behavior
• navigation — SET_CURRENT_ROUTE, SET_CURRENT_BOTTOM_NAV_ROUTE, selectors
• experimentalSettings — SET_SECURITY_ALERTS_ENABLED on/off
• infuraAvailability — BLOCKED/NOT_BLOCKED, getInfuraBlockedSelector, exported constants
• legalNotices — privacy policy actions, idempotent shown-date storage, action creators
• browser/selectors — selectBrowserHistory, selectSearchEngine

Selectors (3 files):

• banner — selectDismissedBanners with memoization check
• browser — history → Recents category (reversed), bookmarks → Favorites category
• bridgeController — selectBridgeControllerState, selectQuoteRequest

Utilities (3 files):

• confirm-tx — gas price calculations, hex comparisons, currency formatting, exponential rounding
• browserScripts — string content checks for injected JS scripts (SPA listener, window info, postMessage)
• accounts — getAccountNameWithENS with ENS/custom name/missing account scenarios

Core constants (2 files):

• MetaMetrics.constants — anonymous ID export
• RatesController/constants — state change event name

Review & Testing Checklist for Human

• confirm-tx.test.js only covers 7/10 exported functions — getValueFromWeiHex, getTransactionFee, and convertTokenToFiat are untested. Decide if these gaps are acceptable or need coverage.
• util/accounts/index.test.ts uses as any casts and simplified mocks for safeToChecksumAddress (lowercases) and isDefaultAccountName (regex). Verify these mocks approximate the real implementations closely enough to be meaningful.
• browserScripts.test.ts and constant tests are shallow — they primarily assert that strings contain substrings or equal hardcoded values. Evaluate whether these provide meaningful regression value or just pad coverage numbers.
• Run yarn test:unit and yarn test:validate-coverage to confirm all tests pass in the full suite and that coverage thresholds are met. Only individual test files were verified locally, not the full suite or coverage validation.
• Planned but missing: bridgeStatusController selector test and util/bridge/index.ts (serializeQuoteMetadata) test were identified as targets but not implemented.

Notes

• Link to Devin run: https://app.devin.ai/sessions/bbcee77a55a64585a345831342dac8fb
• Requested by: @abhay-codeium
• All 16 test files pass individually when run with npx jest <file> --no-coverage
• Tests follow existing patterns: jest.mock() for dependencies, minimal mocking, edge case coverage

[devin-ai-integration]

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