Week 10 - Monday

11 March 2024

Web Infra - Morning Session

First Hour

Quiz, read the following screenshots and follow their instructions.

Second Hour

We will apply unit tests to our API code for our final project.

We will use the testing frameworks jest and supertest for NodeJS / Express servers. You may use equivalent libraries and metaphors in Python, such as this tutorial.

Installing dependencies

Change to your final project directory. Don't worry, nothing will be changed about your existing code, only a new test-only directory will be added, and some (dev) dependencies in package.json

npm i -D test supertest

After you install dependencies, your package.json should look similar to this. An important line you'll need to add is the test command in the scripts key, that runs jest in the current directory.

  "scripts": {
    "test": "jest .",

You should also install the jest command as a global binary, that you can share across all projects.

npm i -g jest

and then check you can run it

which jest

should return the location of the jest file on your system, not an empty line.

Create a tests directory

mkdir tests

Try a basic unit test

You'll create two new files, a simple dummy module that exports one simple function to-be-tested, and a unit test for it. They will be named and located as follows

├── src
│   ├── double.js
├── tests
│   ├── double.test.js

First, try putting the first version of this code in a new file in your src directory, or somewhere you can easily import it, called double.js.

// not testable
const value = 100;
const double = () => {
  return value * 2;
};

module.exports = {
  double
}

It is meant to be simple and unrelated to your code at first.

In your new test directory, write a unit test for it using Jest in a file called double.test.js

const { double } = require('../src/double.js');

describe("double function", () => {
  it("should return twice its argument", async () => {
    // .,...

    expect(double(25)).toBe(50);
  });
});

Running and seeing errors

Now try running all tests that are findable, by typing and pressing enter

npm test

You'll see the above error at first.

What causes it? Discuss with a pair programming partner, then iterate:

• discuss the root cause of the problem, suggest a modification.
• make the modifications
• when you both agree there is an 80% chance of success, run npm test again
• repeat

API Unit Testing

Now type in the following Javascript (not Typescript) file into a new tests/postSignUp.test.js file

const { app } = require("../src/server");
const { request } from "supertest";

describe("POST /signup", function () {
  it("responds with json", async () {
    const res = await request(app)
      .post("/signup")
      .send({ username: "hello", password: "hola" })
      .set("Accept", "application/json")

    expect(res.headers["Content-Type"]).toMatch(/json/);
    expect(res.status).toEqual(200);
  });
});

Start your Express server, including any SSH tunnel needed to your database, and in a separate terminal, run the test.

npm test

With a pair programming or team partner, iterate the same procedure to make progress towards the test passing.

• discuss the root cause of the problem, suggest a modification.
• make the modifications
• when you both agree there is an 80% chance of success, run npm test again
• repeat

You may start a dev diary with screenshots and error stack traces to document your process, in place of having a code interview.