reduce_test.ts

import { test } from "@cross/test";
import { assertEquals } from "@std/assert";
import { assertType, type IsExact } from "@std/testing/types";
import { reduce } from "./reduce.ts";

await test("reduce with initial", () => {
  const accumulators: number[] = [];
  const values: number[] = [];
  const indices: number[] = [];
  const result = reduce([1, 2, 3, 4, 5], (acc, value, index) => {
    accumulators.push(acc);
    values.push(value);
    indices.push(index);
    return acc + value;
  }, 5);
  assertEquals(result, 20);
  assertEquals(accumulators, [5, 6, 8, 11, 15]);
  assertEquals(values, [1, 2, 3, 4, 5]);
  assertEquals(indices, [0, 1, 2, 3, 4]);
  assertType<IsExact<typeof result, number>>(true);
});

await test("reduce without initial", () => {
  const accumulators: number[] = [];
  const values: number[] = [];
  const indices: number[] = [];
  const result = reduce([1, 2, 3, 4, 5], (acc, value, index) => {
    accumulators.push(acc);
    values.push(value);
    indices.push(index);
    return acc + value;
  });
  assertEquals(result, 15);
  assertEquals(accumulators, [1, 3, 6, 10]);
  assertEquals(values, [2, 3, 4, 5]);
  assertEquals(indices, [1, 2, 3, 4]);
  assertType<IsExact<typeof result, number | undefined>>(true);
});

await test("reduce without initial / with empty iterable", () => {
  const result = reduce([] as number[], (acc, v) => acc + v);
  assertEquals(result, undefined);
  assertType<IsExact<typeof result, number | undefined>>(true);
});