RewirableObject

Request.spec.ts

import { Request, rewireRequest } from "./Request";

const mockRequest = { fake: true };
rewireRequest(mockRequest);

// Use mocked request here

Request.ts

import * as request from "request";
import { RewirableObject } from "./RewirableObject";

const rewirable = new RewirableObject(request);
export const rewireRequest = rewirable.rewire;
export type requestType = typeof request;
export const Request = rewirable.get() as requestType;

RewirableObject.ts

/**
 * Create a proxy object that can be replaced unbeknown to external modules for testing purposes
 *
 * This should be used to replace side-effecty modules like Log, etc. It can be used like:
 *
 * import {RewirableObject} from "./RewirableObject";
 *
 * const rewirable = new RewirableObject(mySideEffectyObject);
 * export const rewireMySideEffectyObject = rewirable.rewire;
 * export const MySideEffectyObject = rewirable.get() as typeof mySideEffectyObject;
 */
export class RewirableObject {

    private instance: any;
    private proxyInstance: any;

    constructor(instance: any) {
        this.instance = instance;
        const that = this;
        const rewireHandler = {
            get(target: any, name: string) {
                return that.instance[name];
            },
            apply(target: any, thisArg: any, argumentsList: any) {
                return that.instance.apply(thisArg, argumentsList);
            },
        };

        this.proxyInstance = new Proxy({}, rewireHandler);

        this.get = this.get.bind(this);
        this.rewire = this.rewire.bind(this);
    }

    public get() {
        return this.proxyInstance;
    }

    public rewire(newInstance: any) {
        this.instance = newInstance;
    }
}