sj-freitas/forofa

const { reduce } = require("../reduce");

describe("reduce function", () => {
  it("Reduces an array to a Sum", () => {
    const array = [10, 20, 30, 20, 10, 9];

    const sum = reduce(array, (prev, next) => prev + next);

    expect(sum).toEqual(99);
  });

  it("Reduces an array to a Sum with an initial value", () => {
    const array = [1, 2, 3, 5, 8, 13];

    const sum = reduce(array, (prev, next) => prev + next, 10);

    expect(sum).toEqual(42);
  });

  it("Reduces an array to a Sum with index parameter", () => {
    const array = [1, 2, 3, 5, 8, 13];

    const sum = reduce(array, (prev, next, idx) => idx * (prev + next));

    expect(sum).toEqual(1245);
  });

  it("Reduces an array with just one element returns the first", () => {
    const array = [1];

    const sum = reduce(array, (prev, next) => prev + next);

    expect(sum).toEqual(1);
  });

  it("Reduces an array without elements throws exception", () => {
    const reduceOnEmptyArray = () => reduce([], (prev, next) => prev + next);

    expect(reduceOnEmptyArray).toThrow(TypeError);
    expect(reduceOnEmptyArray).toThrow(
      "Reduce of empty iterable with no initial value"
    );
  });

  it("Reduces an array without elements but initial value returns value.", () => {
    const sum = reduce([], (prev, next) => prev + next, 3);

    expect(sum).toEqual(3);
  });
});