better-dependency-injection-with-laconia

lambda.spec.js

const { handler } = require("./lambda");

let twitterService;

beforeEach(() => {
  // Creates a mocked twitterService
  twitterService = {
    getLatestTweets: jest.fn().mockReturnValue(Promise.resolve())
  };
});

it("should get tweets for user 1000", () => {
  // Runs your exported handler function with the mocked dependencies
  handler.run({ twitterService });
  expect(twitterService.getLatestTweets).toBeCalledWith(1000);
});