Let’s get our test ready to roll by getting our API server and database started and in a clean state. Because our tests and server both run in node, we can do this all using the utilities that Jest exposes for us like beforeAll and afterAll. Then we’ll get a test started and fire a request to the API to make sure we can communicate with the server.

Test Node.js Backends

Start a Node Server and Fire a Request to an HTTP API Endpoint

Instructor: [00:01] For this one, we're going to have a bunch of things we're going to import here. Thank you, Marty the Money Bag. We've got `axios` to make a request to the server we're going to start up. We have `resetDb`, which basically all this is doing is it's calling drop on all of our databases here so that our database is clean and fresh between every one of our tests.

#### auth.exercise.js

```javascript
import axios from "axios";
import { resetDb } from "utils/db-utils";
```

[00:20] Depending on your situation, you may not be able to do this, especially if you have a shared database that you're running your tests against because then one person could be running the test while another person is running the test, and you can mess each other up. That's not really an optimal situation.

[00:33] You'd prefer to stick your database in a Docker container or something like that, have it locally on your machine. If that's not feasible for you, then you need to be a little bit more surgical about how you're cleaning things up.

[00:43] This is a quick and easy way to get things all cleaned up between every one of our tests. We're going to be using `resetDb` between each one of our tests. Then, here we have `generate` so we can generate a login form later and `startServer`, of course, to get our server up and started. That's what we're going to do here.

```javascript
import * as generate from "utils/generate";
import startServer from "../start";
```

[00:58] First, I'm going to declare `server` right here because we need to start the server before all of our tests and then stop the server after all of our tests. Those will be in two different hooks. I'm going to declare that variable up here so we can share that variable between those two hooks.

```javascript
let server;
```

[01:13] We'll start with a `beforeAll`. Before all of our tests, we're going to say `server = await startServer` . Let's copy that from Marty the Money Bag. Thank you.

[01:22] This is an `async` operation, so we're going to do `async` on our function here.

```javascript
beforeAll(async () => {
  server = await startServer({ port: 8000 });
});
```

That way, Jest will wait until the promise that's returned from this callback resolves before it continues on with our test, which is important because it may take a second to start up that server.

[01:36] Then we'll do `afterAll`. This one, we need to close down the server, so that'll be `server.close`. This is also an `async` operation, so we'll do `await`. That means we need `async` right here. That way, before Jest says that the tests are all done, it waits for the promise that's returned from this function to resolve before it wraps up the test.

```javascript
afterAll(async () => await server.close());
```

[01:57] Now, because this is the only thing we're doing in here -- we're not assigning anything like we are in this one -- we can actually write this a little bit more tersely thanks to arrow function implicit return. We'll do that. I like the way that looks better.

```javascript
afterAll(() => server.close());
```

[02:08] Now, before each test, we want our database to be all reset and ready to go. I'm going to add a `beforeEach`. We'll do `await` `resetDb` because that's an `async` function. We'll do `async` here.

```javascript
beforeEach(async () => await resetDb());
```

[02:22] Again, we can do an implicit return thanks to the power of implicit returns on arrow functions. That will return the promise that's returned from `resetDb`. Therefore, Jest will wait for the database to be reset before it runs our tests.

```javascript
beforeEach(() => resetDb());
```

[02:35] Now, with all of that, let's go ahead and make sure that we have the database all set up and we're ready to start making requests, by making our first request with `axios.post` to this URL, so I'll copy that.

```javascript
test('auth flow', async () => {
   axios.post('http://localhost:8000/api/auth/register', {
  })
```

[02:47] We need to pass in a `username` and `password`, so we're going to grab `generate.loginForm` from here. That's going to give us a `username` and a `password` that we can use for this registration. We'll use `username` and `password`, and let's get our result back. This is an `async` operation, so we're going to `await` that.

[03:07] We'll get a `response` right here. Let's go ahead and `console.log(response.data)`.

```javascript
test('auth flow', async () => {
  const {username, password} = generate.loginForm()

  // register
  const response = await axios.post('http://localhost:8000/api/auth/register', {
    username,
    password,
  })

  console.log(response.data)
```

We'll save that, pop this open, and boom! We're getting exactly what we need from that request. Our server is indeed getting started up.

![Endpoint success](https://res.cloudinary.com/dg3gyk0gu/image/upload/v1575572534/transcript-images/24_scikit-learn-start-a-node-server-and-fire-a-request-to-an-http-api-endpoint-endpoint-success.jpg)

[03:21] If we hit enter, we're going to see that our `username` is getting generated by this `loginForm`, and the `id` is getting generated, as well as the `token`. It looks like everything's working so far for this registration end-point.

![Username generated](https://res.cloudinary.com/dg3gyk0gu/image/upload/v1575572534/transcript-images/24_scikit-learn-start-a-node-server-and-fire-a-request-to-an-http-api-endpoint-username.jpg)

[03:33] In review, what we've done so far is, we import all of the things that we need for the setup, for this integration test, and then we start the server up and close it down before and then after all of the tests. Between each one of the tests, we get our database reset.

[03:49] For the first part of our test, we generate a login form which consists of a `username` and `password`. We pass that data to the registration end-point on the server, which we're running on `localhost` at port `8000`, as we defined here. We wait for that to finish up, and we get a response back that has our data. That data consists of the `id`, the `username`, and the `token`.


Backends hold so much of our application's business logic that is often used to support multiple clients (web, mobile, and other native platforms). This logic is critical to get right and deploying a breaking change to this can be devastating to your company's goals (not to mention the bottom-line). Increasing your "deployment confidence" is crucial and automated testing is the best way to do that.

As Node.js continues to grow in usage around the world, learning how to test this mission-critical code in a way that increases developer velocity as well as confidence becomes increasingly important. In this workshop we use an Express.js example and focus on the patterns and practices that you need to learn so you can apply what you learn to test your code written in any Node.js web framework.

You'll learn:

Intro to Test Node.js Backends

Of all things you can test, the easiest thing you can test is a pure function because they require no setup or teardown. In this exercise, we’ll explore testing a pure function called isPasswordAllowed.

Test Pure Functions Overview

Let’s write the basic tests for our simple isPasswordAllowed function to ensure that both valid and invalid passwords receive the correct return value.

Write Unit Tests for a Simple Pure Function

One of the most crucial things you can do when writing tests is ensuring that the error message explains the problem as clearly as possible so it can be addressed quickly. Let’s improve our test by generating test titles so error messages are more descriptive.

Improve Error Messages by Generating Test Titles

Jest has a test-generation feature built-in called test.each which is great, but I don’t particularly like it’s API. Instead, we’re going to use an open source project called jest-in-case which gives us a really nice API for generated tests and improved error messages. Let’s try that library out for our isPasswordAllowed tests here.

Use jest-in-case to Reduce Duplication and Improve Test Titles

Even with jest-in-case there can be a little boilerplate and you can easily side-step that by creating a simple function that allows you to write test cases that are more suited for your use case. Let’s give that a try!

Create a Casify Function to Generate Cases for jest-in-case

There are various types of middleware and for many of them you write tests for them in the same way, so let’s get a look at one of these and try our hand at writing some tests for it.

Test Node Middleware Overview

We have an error middleware in our app for handling uncaught errors throughout our application. Let’s write our first test case for handling an UnauthorizedError which our authentication abstraction throws when someone attempts to access data they shouldn’t.

Write a Unit Test for Handling an UnauthorizedError

Our next test will be really similar to the first. This time we want to handle the case where a response has already been sent which you know if the res.headersSent property is set. So we’ll add that property to our fake response object and verify the middleware behaves correctly.

Write a Unit Test for Handling headersSent in an Error Middleware

Our final case is the fallback scenario where we don’t know exactly why things are failing. In this situation we’ll just give all the information that we can and hopefully the developers can figure out what that is. Let’s write a test case for that situation.

Write a Unit Test for Status 500 Error Middleware Fallback

We’ve got a little bit of duplication between these tests and in a more complex middleware we’ll have a lot of duplication. The duplication itself isn’t necessarily problematic. The problem comes in the form of readability of our tests. When there’s a great amount of duplication, it makes it harder to identify the parts of the test that distinguishes it from other tests. In this lesson we’ll apply the object factory pattern to reduce duplication and make it easier to maintain our tests.

Improve Test Maintainability using the Test Object Factory Pattern

We’re going to need the same utilities for our object factories in several places in our tests, so let’s use some pre-built utilities instead of the ones we wrote for this file.

Use a Test Object Factory utils/generate

Controllers are a collection of middleware that applies business logic specific to your domain. Typically these are tested like any other middleware, but often they require mocking the database for unit tests.

Test Node Controllers Overview

Let’s write our first controller middleware unit test by mocking out a database call and verifying that the database is interacted with correctly and the response is sent correctly.

Write a Unit Test for a Controller by Mocking the Database

Let’s add a test for an edge case that responds with an error message. In this lesson we’ll talk about the value of using the toMatchInlineSnapshot assertion for error messages.

Simplify Assertions on Error Messages with toMatchInlineSnapshot

Not all controller middleware send responses. In this unit test, we’ll verify that a controller’s middleware interacts with the request, response, next function, and database correctly.

Unit Test Business Logic of a Controller’s Middleware

Sometimes people try to access data that’s not there and it would be great if our server doesn’t fall over when they do, so we have some code to handle that case. Let’s get that tested and use toMatchInlineSnapshot for asserting on the error message.

Test Controller 404 Edge Case where Resource is Not Found

If the user tries to access a resource they shouldn’t have access to, we need to make sure they can’t get that resource, and we’ll want a test to make sure that functionality doesn’t break because this is a data security concern. In this one we handle dynamic data in a snapshot by making a consistent ID for the user and list item.

Test Controller Unauthorized Case

We have another controller function we want to test that will retrieve all of the user’s list items. For this one we’ll need to mock out a few new APIs and build multiple books and list items. Then we’ll have to do a few things to ensure that the APIs were called correctly.

Test getListItems for Getting Multiple Mock Objects

We want to test the createListItem controller function so we can ensure that users can create new list items. In this one we need to mock out several database requests. We also see how great Jest error output is which helps us identify a few mistakes that we made really easily.

Test the Happy Path of a Creation Flow

Even though your edge cases don’t run as often as your happy path cases, they are important to test to make sure you handle those correctly. In this one we’ll verify that if a user attempts to create a new list item for a book even though they already have a list item for that book.

Testing an Error Case for createListItem

For this one, we’ll need to have an existing listItem and we’ll create some new notes for it. Then we’ll have the original list item and the updated list item and ensure that our API is being called with the right version of the list item.

Testing the Happy Path for updateListItem

This one’s a bit unique because it’s pretty simple. All we need to do here is verify that the remove method of our was called properly, but we don’t need to bother mocking out what it returns because our code doesn’t use that return value. We also want to verify that the res.json was called properly, so we’ll do that as well.

Testing Resource Deletion

Let’s start doing some server integration tests. We’ll get our server started and database going so we can hit the endpoints in the same way clients will be using our endpoints. Let’s explore how our app is started so we can start it in our test environment and I’ll show you around the codebase so you can navigate around while you test things out.

Test Authentication API Routes Overview

When you’re interacting with the API response of a server, some of the data you receive is information that you cannot assert on directly. In this lesson we’ll talk about how to use Jest’s asymmetric matchers to assert on the type of data your server is sending.

Make Assertions on HTTP API Responses for Registration

Let’s make another request in this same test to the login endpoint with the same post data as we used for registration. Then we can verify that the information we retrieved from the registration request is the same as the information we retrieved from the login request.

Test the Login Endpoint for a Node Server

Our server has an API for authenticated clients to request information for the currently logged in user. Let’s make an authenticated request using the user token we retrieved from the login request to get confidence that the token generated will get the data for the user.

Test the User’s Resource Endpoint

We’ve got a bit of duplication in our test for each request and it’d be nice to remove that, so we’ll create a pre-configured axios client to reduce that duplication.

Create a Pre-configured axios Client for the baseURL

If our request fails, the error message is really useless. The server sends us back a much more useful error message, but by default Jest wont display that error properly and we can’t identify the line of code that made the failing request. Let’s use a custom axios interceptor which will improve those error messages considerably by displaying the response that the server returned.

Improve Error Messages with an axios Interceptor

If you want to run your tests in parallel and each of your tests starts up the server on its own, then you could run into a problem where two servers try to bind to the same port. To avoid this, we can use the JEST_WORKER_ID environment variable so we can ensure that the port our server starts on is unique. Let’s try that out.

Ensure a Unique Server Port

Let’s test the case where we try to register two users of the same username. We’ll first register a user, and then we’ll attempt to register a second user with the same username and assert on the error message. We’ll use toMatchInlineSnapshot on the error that’s returned and Jest will serialize that like a champ.

Use Snapshots to Assert on Server Error Responses

Often in integration tests you’ll have situations where you are over testing. Sometimes that’s acceptable, but you can speed up your tests by getting your application into a testable state a little quicker. In this lesson we’ll skip hitting the API for our setup and instead interact directly with the database.

Interact Directly with the Database

Integration tests are typically best for common cases and you can cover other cases using lower level tests, but I thought it’d be interesting to show you how to cover a few other edge cases as well in this lesson.

Test all the Edge Cases

Things change a little bit when we want to hit an endpoint that requires the user to be authenticated. For this exercise you’ll need to use an authenticated test with a test user that’s already in the database. Then you can use that test user for each of the operations you do on the list item resource (Create, React, Update, Delete).

Test CRUD API Routes Overview

Let’s get a test user and authenticated axios client, and then we’ll need to generate a book and insert that into the database directly so we can create a list item for our test user for that book. Then we can verify that the response data is correct.

Write an Integration Test for a Resource Create Endpoint

Now that we’ve created a list item, let’s try to read that list item. This will give us confidence that the list item we created was actually saved to the database and can now be retrieved.

Write an Integration Test for a Resource Read Endpoint

For the update, we’ll need to create new notes for our list item and send those updates to the updates endpoint. Then we can verify that the response we get back is the same as the original list item except with the updated notes.

Integration Test a Resource Update Endpoint

For our delete endpoint, we don’t need to do too much beyond hitting the endpoint, but it could be problematic if we just hit the endpoint and verify the response. In this lesson we’ll find out why that is and how we can use our test to make sure that the item was actually deleted from the database.

Integration Test a Resource Delete Endpoint

Typically, it’s nicer to use toMatchInlineSnapshot for error messages, but sometimes the contents of the error message are generated. But I’ve got a little trick for solving this problem that you’ll probably find useful.

Start a Node Server and Fire a Request to an HTTP API Endpoint

Transcript

Start a Node Server and Fire a Request to an HTTP API Endpoint