binary.spec.js

import { binary } from './binary.js'

test('happy', () => {
  const result = binary(function (
    x, y, z
  ){
    expect(arguments).toHaveLength(2)
    expect(z).toBeUndefined()
    expect(x).toBe(10)
    expect(y).toBe(20)

    return x + y
  })(
    10, 20, 30
  )
  expect(result).toBe(30)
})