testMyModule.js

"use strict";

const myModule = rehire("./myModule", {
    "fs": { existsSync: () => true },
});

suite("myModule", () => {

    afterChunk(() => {
        myModule.__reset__();
    });

    test("mock internal function", () => {

        chunk("get it", () => {
            const _summarize = myModule.__get__('_summarize');
            expect(_summarize(1, 2)).to.be.equal(3);
        });

        chunk("set it", () => {
            myModule.__set__('_summarize', () => 5);
            expect(myModule.summarize(1, 2)).to.be.equal(5);
        });
    });

    test("mock third-party module", () => {

        chunk(() => {
            expect(myModule.isPathExists('/bla/bla/bla')).to.be.true;
        });
    });
});