Professional Testing With Javascript

Introduction

As you can imagine it gets a bit unwieldy to have hundreds of if statements throughout your code. Beyond them being just a bit large, they lack organization when categorizing features and they also can be somewhat difficult to read. All of these problems are amplified when there are so many!

For many years, if statements were all we had. So, we kept using them. In the past few years, programmers have created a bunch of new testing tools to make testing easier when dealing with many many, many, many tests. The main one we are going to be using is called Mocha.

Let's walk through the basics of testing. You'll discover it's not too different from what you've experienced in the last few lessons. Many lessons going forward will include tests. We refer to these lessons as labs. By having tests in our lesson materials, you can apply what you're learning and get immediate feedback on your code!

Getting Started

First things first, open up index.js in your terminal. You are going to see mostly familiar things:

var name = "Joe"
var height = "74"
var message = `${name} is ${height} inches tall`

module.exports = {name, height, message}

This should look familiar except for that third line:

var message = `${name} is ${height} inches tall 

It's actually pretty cool what that line does. Explore what ends up in the message variable by typing console.log(message) on the last line and then run your index.js file. You should see "Joe is 74 inches tall". Pretty cool right? If you create a string wrapping it in back-ticks (`) you can then use your variables directly in the string to create a sentence like we just did.

The key is when you use a variable you have to wrap the variable itself in the ${ and }. If you were to modify message to look like this:

var message = `name is height inches tall

...and run your code again you'd get "name is height inches tall". That's not what you want! The ${ and } tell Javascript to grab the value inside the variable, not just that variable name.

The Tests

We have our code, now let's take a look at the tests. They are located in the example-test folder inside a file named index-test.js. In this lesson we are going to go over all of the tests, and then show you how to run them in the next lesson.

var index = require("../index.js")

/*

describe("what-is-a-test", () => {
  describe("Name", () => {
    it('returns "Susan"', () => {
      expect(index.name).toEqual("Susan")
    })
  })


  describe("Height", () => {
    it("is less than 40", () => {
      expect(index.height).toBeLessThan(40)
    })
  })

  describe("Message", () => {
    it("gives the name and height", () => {
      expect(index.message).toInclude(index.name)
      expect(index.message).toInclude(index.height)
    })
  })

})

*/

The first thing you'll notice is that all of the code is commented out using the /* and */ block commenting syntax. This is because we will get into actually running the tests in the next lesson. This lesson, let's just walk through what you are seeing. In the next lesson the /* and */ will be removed.

There is a lot here. Right now, you really just need to focus on a few different lines. The first grouping is testing our name variable.

  describe('Name', () => {
    it('returns "Susan"', () => {
      expect(index.name).toEqual('Susan')
    })
  })

If you look at the line that begins with expect you'll see this: expect(index.name).toEqual('Susan'). Read outloud, we get "Expect index.name to equal Susan". That's exactly what it's saying! If we continue down to the Height section you'll see this code:

  describe("Height", () => {
    it("is less than 40", () => {
      expect(index.height).toBeLessThan(40)
    })
  })

The interesting line here is expect(index.height).toBeLessThan(40). If you read that one out as "Expect index.height to be less than 40" you'd be correct! Let's look at the final one:

  describe("Message", () => {
    it("gives the name and height", () => {
      expect(index.message).toInclude(index.name)
      expect(index.message).toInclude(index.height)
    })
  })

This one has two expect statements. If you read them out as English you'll discover that the tests expects index.message to include both index.name and index.height.

OK Great. You now understand what the tests are saying. Let's run our tests and submit our code to learn. In the terminal first type learn. You should get a message saying 0 passing and the local build light will turn green.

For future labs, once all tests are passing, type learn submit in the terminal to submit your code and register completion. However, in this particular lesson, you will need to make a small edit to one of the files before running learn submit and continuing on. This is because Learn expects labs to include student written code.

To register completion in this lab, make a small edit to any of the files present. If you added console.log(message) to index.js earlier, then you already completed this task. Run learn submit now and Learn will recongize that the contents of your lesson are slightly different than the original contents and will register completion of the lesson.

You should be good to go forward now! In the next lesson we are going to cover how to run them, and then have you actually solve the lab!

View What Is A Test on Learn.co and start learning to code for free.