How To Mock a Node Module Which Provides Function using Jest

//app.js (This is a target of testing.)
const moduleA = require("./moduleA.js")();

module.exports = (()=>{
    console.log(moduleA.showValue());
    moduleA.add(10);
    console.log(moduleA.showValue());
})();

//moduleA.js (External library like a web API and database module)
const moduleA = require("./moduleA.js")();

module.exports = (()=>{
    console.log(moduleA.showValue());
    moduleA.add(10);
    console.log(moduleA.showValue());
})();

//app.test.js (BAD CASE)

const moduleA = require('../moduleA.js')();
jest.mock('../moduleA.js', () => () => {
    return  {
        add: jest.fn(),
        showValue: jest.fn().mockImplementation(() => 1000)
    };
});

describe("app", () => {
    test("", () => {
        require("../app.js");
        expect(moduleA.add).toHaveBeenCalled(); //----->Failed. jest says add has never been called.
        expect(moduleA.showValue).toHaveBeenCalled();
    });
});

//app.test.js (GOOD CASE)

const moduleA = require('../moduleA.js')();
jest.mock('../moduleA.js', () => () => {
    this.instance = this.instance || {//---> This mock should be singleton.
        add: jest.fn(),
        showValue: jest.fn().mockImplementation(() => 1000)
    };
    return this.instance;
});

describe("app", () => {
    test("", () => {
        require("../app.js");
        expect(moduleA.add).toHaveBeenCalled(); //-----> Pass!
        expect(moduleA.showValue).toHaveBeenCalled();//-----> Pass!
    });
});

Here is all source code.
github.com