NodeJS + Typescript AWS Lambda 上的单元测试

Question

Which one is the best way to unit test a lambda implemented in NodeJS using TypeScript like this dummy one:

import {Callback} from "aws-lambda";

export interface BinaryEvent {
  number1: number
  number2: number
}

export interface Result {
  result: number
}

export type BinaryOperation = (number1: number, number2: number) => number;

export type BinaryOperationHandler = ({number1, number2}: BinaryEvent, context: any, callback: Callback<Result>) => void;

export const addition: BinaryOperationHandler = ({number1, number2}, context, callback) => {
  setTimeout(() => callback(null, {result: (number1 + number2)}), 1000);
}

Answer 1

I managed to find a way to unit testing using jest using jest.fn() like this:

import {addition} from "./index";

it('Sums 2 numbers', async() => {
  const number1 = 3, number2 = 2, callback = jest.fn();
  await addition({number1, number2}, {}, callback);
  expect(callback.mock.calls.length).toBe(1);
  expect(callback.mock.calls[0][1].result).toBe(number1 + number2);
})

A complete working dummy example is available in the github repo: https://github.com/jvillane/aws-sam-lambda-jest-unit-test