@arrows/array/src/prepend_.test.ts

Functional tools for JS arrays

import { prepend_ } from "./index"

describe("Array prepend", () => {
  it("returns array with additional element at the beginning", () => {
    const arr = [2, 3, 4]

    const result = prepend_(1, arr)
    const result2 = prepend_(1)(arr)

    const expected = [1, 2, 3, 4]

    expect(result).toEqual(result2)
    expect(result).toEqual(expected)
  })

  it("always returns a new array", () => {
    const arr = [2]
    const result = prepend_(1)(arr)

    expect(result).not.toBe(arr)
  })
})