Set up frontend test infrastructure

Install @testing-library/react, @testing-library/jest-dom,
@testing-library/user-event, and jsdom. Configure Vitest with globals,
jsdom environment, and a setup file importing jest-dom matchers. Add a
custom render helper wrapping components with QueryClientProvider and
MemoryRouter. Exclude e2e/ from vitest. Smoke test covers
formatEvolutionMethod.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/test/setup.ts

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+import '@testing-library/jest-dom'

frontend/src/test/utils.tsx

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+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { render, type RenderOptions } from '@testing-library/react'
+import { type ReactElement } from 'react'
+import { MemoryRouter } from 'react-router-dom'
+
+export function createTestQueryClient(): QueryClient {
+  return new QueryClient({
+    defaultOptions: {
+      queries: { retry: false, gcTime: Infinity },
+      mutations: { retry: false },
+    },
+  })
+}
+
+function AllProviders({ children }: { children: React.ReactNode }) {
+  const queryClient = createTestQueryClient()
+  return (
+    <QueryClientProvider client={queryClient}>
+      <MemoryRouter>{children}</MemoryRouter>
+    </QueryClientProvider>
+  )
+}
+
+function customRender(ui: ReactElement, options?: Omit<RenderOptions, 'wrapper'>) {
+  return render(ui, { wrapper: AllProviders, ...options })
+}
+
+export * from '@testing-library/react'
+export { customRender as render }

frontend/src/utils/formatEvolution.test.ts

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+import { formatEvolutionMethod } from './formatEvolution'
+
+const base = { minLevel: null, item: null, heldItem: null, condition: null }
+
+describe('formatEvolutionMethod', () => {
+  it('formats level-up with a min level', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'level-up', minLevel: 16 })).toBe('Level 16')
+  })
+
+  it('formats level-up without a min level', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'level-up' })).toBe('Level up')
+  })
+
+  it('formats use-item trigger', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'use-item', item: 'fire-stone' })).toBe(
+      'Fire Stone'
+    )
+  })
+
+  it('formats trade trigger', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'trade' })).toBe('Trade')
+  })
+
+  it('formats unknown trigger by capitalizing words', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'shed-skin' })).toBe('Shed Skin')
+  })
+
+  it('appends held item', () => {
+    expect(formatEvolutionMethod({ ...base, trigger: 'trade', heldItem: 'metal-coat' })).toBe(
+      'Trade, holding Metal Coat'
+    )
+  })
+
+  it('appends condition', () => {
+    expect(
+      formatEvolutionMethod({ ...base, trigger: 'level-up', minLevel: 20, condition: 'at night' })
+    ).toBe('Level 20, at night')
+  })
+
+  it('combines all parts', () => {
+    expect(
+      formatEvolutionMethod({
+        trigger: 'level-up',
+        minLevel: 25,
+        item: null,
+        heldItem: 'kings-rock',
+        condition: 'high friendship',
+      })
+    ).toBe('Level 25, holding Kings Rock, high friendship')
+  })
+})