describe('Form validation', () => {
  it('validates correct form', () => {
    const form = {
      username: 'alice123',
      email: 'alice@example.com',
      password: 'SecurePass123',
      confirmPassword: 'SecurePass123',
    }
    const result = validateForm(form)
    expect(result._tag).toBe('Right')
  })

  it('accumulates all form errors', () => {
    const form = {
      username: 'a!',
      email: 'invalid',
      password: 'weak',
      confirmPassword: 'different',
    }
    const result = validateForm(form)
    expect(result._tag).toBe('Left')
    if (result._tag === 'Left') {
      expect(result.left.length).toBeGreaterThan(3)
    }
  })

  it('detects password mismatch', () => {
    const form = {
      username: 'alice',
      email: 'alice@example.com',
      password: 'SecurePass123',
      confirmPassword: 'DifferentPass123',
    }
    const result = validateForm(form)
    expect(result._tag).toBe('Left')
    if (result._tag === 'Left') {
      expect(result.left).toContain('Passwords do not match')
    }
  })
})