test('paginates results', () => {
  const items = createItems(100)
  const result = paginate(items, { page: 1, pageSize: 10 })

  expect(result.items).toHaveLength(10)
  expect(result.totalPages).toBe(10)
})
// Works for normal case, crashes in production on edge cases

describe('paginate', () => {
  // Happy path
  it('returns requested page of items', () => {
    const items = createItems(100)
    const result = paginate(items, { page: 2, pageSize: 10 })
    expect(result.items).toHaveLength(10)
    expect(result.currentPage).toBe(2)
  })

  // Empty state
  it('returns empty array when no items exist', () => {
    const result = paginate([], { page: 1, pageSize: 10 })
    expect(result.items).toEqual([])
    expect(result.totalPages).toBe(0)
  })

  // Boundary: last page partial
  it('returns partial page when items dont fill last page', () => {
    const items = createItems(25)
    const result = paginate(items, { page: 3, pageSize: 10 })
    expect(result.items).toHaveLength(5)
  })

  // Boundary: page beyond range
  it('returns empty array when page exceeds total pages', () => {
    const items = createItems(10)
    const result = paginate(items, { page: 5, pageSize: 10 })
    expect(result.items).toEqual([])
  })

  // Invalid input
  it('throws when page is zero or negative', () => {
    expect(() => paginate([], { page: 0, pageSize: 10 })).toThrow()
    expect(() => paginate([], { page: -1, pageSize: 10 })).toThrow()
  })

  // Boundary: single item
  it('handles single item correctly', () => {
    const items = createItems(1)
    const result = paginate(items, { page: 1, pageSize: 10 })
    expect(result.items).toHaveLength(1)
    expect(result.totalPages).toBe(1)
  })
})