如何模拟打字稿类的多个功能？

Question

Suppose, I have a typescript class

a.ts

export class A {
    constructor() {
         this.__functionA()
    }

    private __functionA(){
        this.__functionB()
    }

    private __functionB(){
    }

}

Now, I have some tests for my Class

import { A } from "./a"

describe("Class A",() => {

    it(`__functionB should Have been called`,() => {

        A.proptotype.__functionB = jest.fn()
        A.proptotype.__functionA = jest.fn()

        let instance = new A()

        expect (instance.__functionB).toHaveBeenCalled()
        expect (instance.__functionA).toHaveBeenCalled()

    })
})

the tests fail with an error

expect(jest.fn()).toHaveBeenCalled()

Now, when I mock only the __functionA of Class A and run my assertions against only that function , ie expect (instance.__functionA).toHaveBeenCalled() , my test pass. Why so?

And How can I mock more than one functions of a Class ?

Correct me, if I am doing something wrong here.

NB:- I am using jest to run my tests .

Answer 1

Found the answer,

I just had to replace

A.proptotype.__functionB = jest.fn()
A.proptotype.__functionA = jest.fn()

with

jest.spyOn(A.proptotype,__functionA)
jest.spyOn(A.proptotype,__functionB)

and everything works fine.

Hope, this helps someone.