jest.spyOn

foo-bar.test.ts

import {foo, bar} from '../foo-bar';
import * as abc from '../util'
import * as https from 'https'

describe("asdf", () => {
    test("foo", async () => {
        jest.spyOn(https, 'request').mockImplementation(() => jest.fn() as any);
        await foo('https://example.org');
        expect(https.request).toHaveBeenCalledWith('https://example.org');
    })

    test("bar", () => {
        jest.spyOn(abc, 'add').mockImplementation(() => 1234);
        expect(bar()).toBe(1234)
        expect(abc.add).toHaveBeenCalledWith(1, 2);    
    })
})

foo-bar.ts

import {request as httpsRequest} from 'https';
import { Socket } from 'net';
import { add } from './util';

export const foo = async (url: string = "https://example.org") => {
    return new Promise((resolve, reject) => {
        const request = httpsRequest(url);
        request.once('socket', (socket: Socket) => {
            if(socket.connecting) {
                socket.once('lookup', () => { console.log(process.hrtime())});
            }
        });

        request.on("response", (response) => {
            let chunks: Buffer[] = [];
            let bufferLength = 0;
      
            response.on("error", reject);
      
            response.on("data", (data: any) => {
              bufferLength += data.length;
              chunks.push(data as Buffer);
            });
      
            response.on("end", () => {
              response.body = Buffer.concat(chunks, bufferLength).toString("utf8");
              chunks = [];
              bufferLength = 0;
      
              if (response.statusCode == null) {
                response.statusCode = 0;
              }
      
              resolve(response);
            });
        });
      
          request.on("error", (err: Error) => {
            reject(new Error(err.message));
          });
      
          request.end();
    })
};

export const bar = () => {
    return add(1, 2);
}

issue-in-jest#spyOn.md

Unable to make the spyOn method to make the spying work for https.request() method

Reproduce

• Run the tests in foo-bar.ts
• The test for bar works, when spying on add method from util.ts
• The test for foo doesn't work, when spying on request method from https

util.ts

export const add = (a: number, b: number) => a + b;