rc-js-util/src/map/impl/map-first-key.spec.ts

A collection of TS and C++ utilities to help writing performant and correct applications, achieved through strict typing and (removable) invariant checking.

import { mapFirstKey } from "./map-first-key.js";
import { Test_setDefaultFlags } from "../../test-util/test_set-default-flags.js";

describe("=> mapFirstKey", () =>
{
    beforeEach(() =>
    {
        Test_setDefaultFlags();
    });

    it("| returns the first key where available", () =>
    {
        const values = new Map([["a", 1], ["b", 2], ["c", 3]] as const);
        const result: "a" | "b" | "c" | undefined = mapFirstKey(values);
        expect(result).toEqual("a");
    });

    it("| returns undefined if empty", () =>
    {
        const values = new Map<string, number>();
        const result: string | undefined = mapFirstKey(values);
        expect(result).toEqual(undefined);
    });
});