Jest: How to mock one specific method of a class

Question

Let\'s suppose I have the following class:

export default class Person {
    constructor(first, last) {
        this.first = first;
        this.last = last         


        

Answer 1

Have been asking similar question and I think figured out a solution. This should work no matter where Person class instance is actually used.

const Person = require("../Person");

jest.mock("../Person", function () {
    const { default: mockRealPerson } = jest.requireActual('../Person');

    mockRealPerson.prototype.sayMyName = function () {
        return "Hello";
    }    

    return mockRealPerson
});

test('MyTest', () => {
    const person = new Person();
    expect(person.sayMyName()).toBe("Hello");
    expect(person.bla()).toBe("bla");
});