functional/composition.test.ts

import { identity, nop, partial, pipe } from "./composition.ts";
import { expect, it } from "./deps.testing.ts";

it("nop", () => {
  expect(nop()).toBeUndefined();
});

it("identity", () => {
  expect(identity(5)).toBe(5);
  expect(identity(null)).toBe(null);
});

it("partial", () => {
  const func1 = (conf: { a: number; b: string; c: number }) =>
    `${conf.a}${conf.b}${conf.c}`;
  const pfunc1 = partial({ b: "test" }, func1);
  expect(pfunc1({ a: 5, c: 8 })).toEqual("5test8");

  const func2 = (conf: { a: number; b: string }, c: number) =>
    `${conf.a}${conf.b}${c}`;
  const pfunc2 = partial({ b: "test" }, func2);
  expect(pfunc2({ a: 2 }, 3)).toEqual("2test3");
});

it("pipe", () => {
  const f = pipe((x: number) => x * 2, (x: number) => x + 1);
  expect(f(1)).toBe(3);
  expect(f(2)).toBe(5);
  expect(f(3)).toBe(7);
});