Testing AWS Severless application using Jest - amazon-web-services

Question

I have a basic serverless application below, I want to test using Jest if getUserById method is called. I am also using inversifyjs. Now when I run my test I am getting an error TypeError: Reflect.hasOwnMetadata is not a function. Another thing how can I mock a response here?
handler.spec.ts
import { IUsersHandler } from './../src/IUsersHandler';
import { UsersHandler } from './../src/UsersHandler';
import { APIGatewayProxyResult } from 'aws-lambda';
let handler: IUsersHandler;
let mockResponse: APIGatewayProxyResult;
describe("UsersHandler", () => {
beforeEach(() => {
handler = new UsersHandler();
});
it("should call getUserById method", () => {
const spy = jest.spyOn(handler, 'getUserById').mockImplementation(async () => mockResponse);
expect(spy).toBeCalledTimes(1);
});
});
UsersHandler Class
import { IUsersHandler } from './IUsersHandler';
import { injectable } from "inversify";
import { APIGatewayProxyHandler, APIGatewayProxyResult, APIGatewayProxyEvent } from "aws-lambda";
#injectable()
export class UsersHandler implements IUsersHandler {
constructor() { }
public getUserById: APIGatewayProxyHandler = async (
event: APIGatewayProxyEvent
): Promise<APIGatewayProxyResult> => {
try {
return {
statusCode: 200,
body: JSON.stringify(event)
};
} catch (err) {
return {
statusCode: 500,
body: JSON.stringify(err)
};
}
};
}
User Interface
import { APIGatewayProxyHandler } from 'aws-lambda';
export interface IUsersHandler {
getUserById: APIGatewayProxyHandler;
}
export const TUsersHandler = Symbol.for('IUsersHandler');
Handler.ts
import { IUsersHandler, TUsersHandler } from './src/IUsersHandler';
import { container } from "./src/inversify.config";
import 'source-map-support/register';
export const getUserById = async function (event, context, callback) {
const handler: IUsersHandler = container.get<IUsersHandler>(TUsersHandler);
return handler.getUserById(event, context, callback);
};

Answer 1

Final handler.spec.ts
import "reflect-metadata";
import { IUsersHandler } from "./../src/IUsersHandler";
import { UsersHandler } from "./../src/UsersHandler";
import { APIGatewayProxyEvent, APIGatewayProxyResult } from "aws-lambda";
let handler: IUsersHandler;
let mockEvent: APIGatewayProxyEvent;
let mockResponse: APIGatewayProxyResult;
describe("UsersHandler", () => {
beforeEach(() => {
mockResponse = {
statusCode: 200,
body: "This is a test",
};
handler = new UsersHandler();
});
it("should call getUserById method", async () => {
const spy = jest
.spyOn(handler, "getUserById")
.mockImplementation(async () => mockResponse);
const response: any = await handler.getUserById(mockEvent, null, null);
expect(spy).toBeCalledTimes(1);
expect(response.body).toBe("This is a test");
expect(response.statusCode).toBe(200);
});
});