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skills/testing-next-stack/assets/examples/unit-test.ts

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+import { describe, it, expect, beforeEach, vi } from 'vitest'
+
+/**
+ * Example unit test demonstrating best practices
+ * for testing pure functions and business logic
+ */
+
+// Example function to test
+function validateEntityName(name: string): { valid: boolean; error?: string } {
+  if (!name || name.trim().length === 0) {
+    return { valid: false, error: 'Name is required' }
+  }
+  if (name.length > 100) {
+    return { valid: false, error: 'Name must be 100 characters or less' }
+  }
+  if (!/^[a-zA-Z0-9\s-_']+$/.test(name)) {
+    return { valid: false, error: 'Name contains invalid characters' }
+  }
+  return { valid: true }
+}
+
+describe('validateEntityName', () => {
+  it('accepts valid entity names', () => {
+    expect(validateEntityName('John Doe').valid).toBe(true)
+    expect(validateEntityName("O'Brien").valid).toBe(true)
+    expect(validateEntityName('Location-123').valid).toBe(true)
+  })
+
+  it('rejects empty names', () => {
+    const result = validateEntityName('')
+    expect(result.valid).toBe(false)
+    expect(result.error).toBe('Name is required')
+  })
+
+  it('rejects names with only whitespace', () => {
+    const result = validateEntityName('   ')
+    expect(result.valid).toBe(false)
+    expect(result.error).toBe('Name is required')
+  })
+
+  it('rejects names exceeding max length', () => {
+    const longName = 'a'.repeat(101)
+    const result = validateEntityName(longName)
+    expect(result.valid).toBe(false)
+    expect(result.error).toContain('100 characters')
+  })
+
+  it('rejects names with invalid characters', () => {
+    const result = validateEntityName('Name@#$')
+    expect(result.valid).toBe(false)
+    expect(result.error).toContain('invalid characters')
+  })
+})
+
+// Example async function test
+async function fetchEntityData(id: string): Promise<any> {
+  const response = await fetch(`/api/entities/${id}`)
+  if (!response.ok) throw new Error('Failed to fetch')
+  return response.json()
+}
+
+describe('fetchEntityData', () => {
+  beforeEach(() => {
+    global.fetch = vi.fn()
+  })
+
+  it('fetches entity data successfully', async () => {
+    const mockData = { id: '1', name: 'Test Entity' }
+    ;(global.fetch as any).mockResolvedValueOnce({
+      ok: true,
+      json: async () => mockData
+    })
+
+    const result = await fetchEntityData('1')
+    expect(result).toEqual(mockData)
+    expect(global.fetch).toHaveBeenCalledWith('/api/entities/1')
+  })
+
+  it('throws error on failed fetch', async () => {
+    ;(global.fetch as any).mockResolvedValueOnce({
+      ok: false
+    })
+
+    await expect(fetchEntityData('1')).rejects.toThrow('Failed to fetch')
+  })
+})