[Test Improver] Add unit tests for prefs store

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🤖 This PR was created by Test Improver, an automated AI assistant focused on improving test coverage.

Goal and Rationale

shell/store/prefs.js is the core user-preferences Vuex store for Rancher Dashboard. It had no existing unit tests and contains non-trivial logic:

• getters.theme: strips legacy ui- prefix, resolves auto using the prefers-color-scheme cookie, falls back to 'dark', and lets a management setting override everything
• getters.afterLoginRoute: 6-branch switch that converts a string pref ('home', 'last-visited', '<cluster>-dashboard', or any other name) into a Vue Router location object, consulting authRedirect state and other prefs
• getters.get/getters.options/getters.defaultValue: throw typed errors for unknown keys; all return clones (important for Vue reactivity)
• mutations.reset: clears non-cookie prefs, preserving cookie-backed ones
• actions.setLastVisited: conditional — only tracks the last page when the after-login-route pref is 'last-visited'

Approach

All functions are unit-tested by calling them directly without a real Vuex store — the same pattern used throughout shell/store/__tests__/. Getters receive a constructed state + mocked inner-getter; mutations and actions receive the state directly.

Coverage Impact

Metric	Before	After (file)
Statements	0	~75% of prefs.js
Branches	0	~85% of prefs.js
Functions	0	~80% of prefs.js

Tests Added (35 total)

getters.get (4): unknown-key throw, user-set value, default fallback, clone isolation for objects

getters.defaultValue (3): unknown-key throw, returns default, clone isolation for arrays

getters.options (4): unknown-key throw, no-options throw, correct array returned, clone isolation

getters.theme (6): management setting override, direct theme, ui- prefix stripped, auto→pcs light, auto→pcs dark, auto→dark when pcs empty

getters.afterLoginRoute (7): non-string passthrough, 'home' route, 'last-visited'+authRedirect, 'last-visited'+stored last-visited, 'last-visited' fallback to cluster explorer, 'my-cluster-dashboard' pattern, arbitrary string default

getters.dev (2): returns PLUGIN_DEVELOPER value, falls back to DEV on throw

mutations (7): load, cookiesLoaded, reset clears non-cookies, reset preserves cookies (LOCALE, PREFERS_SCHEME), setDefinition, setAuthRedirect

actions.setLastVisited (3): falsy route early-return, non-last-visited pref early-return, dispatches set when pref is 'last-visited'

Trade-offs

• loadServer and set actions are not tested here — they require a running Vuex store (dispatch with root modules) and are better covered by integration tests.
• loadTheme uses window.matchMedia and setTimeout which require more involved mocking.

Reproducibility

YARN_IGNORE_ENGINES=true NODE_OPTIONS=--max_old_space_size=8192 yarn test:ci shell/store/__tests__/prefs.test.ts

Test Status

✅ 35/35 tests pass
✅ ESLint: no warnings

Warning

Firewall blocked 1 domain

The following domain was blocked by the firewall during workflow execution:

• download.cypress.io

To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
  allowed:
    - defaults
    - "download.cypress.io"

See Network Configuration for more information.

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