describe('Custom Monoids', () => {
  it('finds maximum with MaxMonoid', () => {
    expect(combineMax([3, 7, 2, 9, 1])).toBe(9)
    expect(combineMax([5])).toBe(5)
    expect(combineMax([])).toBe(-Infinity)
  })

  it('flattens arrays with ArrayMonoid', () => {
    const result = flattenArrays([[1, 2], [3, 4], [5]])
    expect(result).toEqual([1, 2, 3, 4, 5])
  })

  it('handles empty nested arrays', () => {
    expect(flattenArrays([])).toEqual([])
    expect(flattenArrays([[], [], []])).toEqual([])
  })
})