Serverless app testing with Jest on Begin

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Paul Chin Jr
March 10, 2020

Testing with Jest

Jest is a super popular and very robust JavaScript testing library. As you likely know, investing in your testing will help you write highly maintainable applications, and help ensure that new code will be less likely to cause regressions.

In this post we’ll demonstrate the basics of testing with Jest on a serverless app in Begin; the example app in this post will achieve the same results as our article about testing with Tap.

Try out testing with Jest right now

Hit this button to deploy a new Node.js + Jest example project to Begin in 15 seconds:

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Testing the libraries

Using Jest’s setup and teardown methods, we will instantiate @architect/sandbox, a local dev environment. Sandbox lets developers work locally by emulating the behavior of API Gateway, Lambda functions, and DynamoDB.

// test/get-index.test.js
let tiny = require('tiny-json-http')
let data = require('@begin/data')
let sandbox = require('@architect/sandbox')
beforeAll(async () => {
  await sandbox.start()
})
afterAll(async () => {
  await sandbox.end()
})

Checking your code with small tests for necessary dependencies will give you confidence that future issues can be tracked down faster.

Testing the GET / route

The first test case makes sure that the application can send a GET request to the project index without any errors. The / route is handled by the Lambda found at src/http/get-index/index.js

// test/get-index.test.js
...
test('get /', async () => {
  let url = 'http://localhost:3333'
  await tiny.get({ url })
})
...

Testing @begin/data

The next two test cases will use Begin Data’s data.set method to create a table called tmp, then it will use the data.get method to make sure that table was created.

// test/get-index.test.js
...
test('data.set', async () => {
  let result = await data.set({table: 'tmp'})
  expect(result.table).toBe('tmp')
  console.log(result)
})
test('data.get', async () => {
  let result = await data.get({table: 'tmp'}
  expect(result.length).toBe(1)
  console.log(result)
})
...

Begin Data is a helpful client library for interacting with DynamoDB. When you start Sandbox, a local in-memory version of DynamoDB starts, making it perfect for running data tests against.

Automate testing with your deploys

Pushing your code to GitHub will automatically run your test suite (and deploy your code to the staging environment). View the results of your latest build’s test output in the Begin Activity view:

Testing with Jest

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Next Steps

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