Add JavaScript unit tests for Redux state management

[GaryJones]

Summary

The JavaScript codebase lacks unit test coverage for critical state management code. Adding tests will prevent regressions and enable confident refactoring.

Scope

Priority 1: Redux Reducers (src/react/reducers/)

• apiReducer - Entry CRUD operations, polling state, error handling
• userReducer - Author selection, config loading
• Test state shape, immutability, edge cases

Priority 2: Redux-Observable Epics (src/react/epics/)

• getEntriesEpic - Pagination, error handling
• pollingEpic - Start/stop, interval handling
• crudEpic - Create/update/delete operations
• Use RxJS marble testing for async flows

Priority 3: React Components

• AuthorSelectOption - Keyboard navigation, focus states
• EntryContainer - Edit mode, delete confirmation
• Use React Testing Library

Technical Approach

# Dependencies already available
npm test -- --coverage

// Example reducer test
describe('apiReducer', () => {
  it('handles GET_ENTRIES_SUCCESS', () => {
    const action = { type: 'GET_ENTRIES_SUCCESS', payload: [entry1] };
    const state = apiReducer(initialState, action);
    expect(state.entries).toHaveLength(1);
    expect(state.loading).toBe(false);
  });
});

Acceptance Criteria

• 80%+ coverage for reducers
• All epics tested with marble diagrams
• Critical user flows covered
• Tests run in CI pipeline

References

• RxJS Marble Testing
• React Testing Library