Test private class method with Jest

getAllUsers.spec.ts

import { Request, Response } from 'express';
import GetAllUsers from './getAllUsers';

describe('Get all users request', () => {
    let mockRequest: Partial<Request>;
    let mockResponse: Partial<Response>;
    let responseObject = {};

    beforeEach(() => {
        mockRequest = {
        };
        mockResponse = {
            statusCode: 0,
            send: jest.fn().mockImplementation((result) => {
                responseObject = result;
            })
        };
    });

    test('200 - users', async () => {
        const expectedStatusCode = 200;
        const expectedReponse = {
            users: [
                {
                    name: 'JOHN',
                    age: 30
                },
                {
                    name: 'Peter',
                    age: 40
                }
            ]
        };

        const userRoute = new GetAllUsers();
        let spy = jest.spyOn(userRoute, 'changeUserName' as any);

        userRoute.handle(mockRequest as Request, mockResponse as Response);

        expect(mockResponse.statusCode).toBe(expectedStatusCode);
        expect(responseObject).toEqual(expectedReponse);

        expect(spy).toHaveBeenCalledWith("John");
        expect(spy).toHaveBeenCalledTimes(1);
    });
});

getAllUsers.ts

import { Request, Response } from 'express';

class GetAllUsers {
    public handle(request: Request, response: Response) {
        const users = [
            {
                name: this.changeUserName('John'),
                age: 30
            },
            {
                name: 'Peter',
                age: 40
            }
        ]

        response.statusCode = 200;
        response.send({ users });
    }

    private changeUserName(userName: string) {
        return userName.toUpperCase();
    }
}

export default GetAllUsers;