Functions Lab

Practice writing code to make tests pass!

Getting Started

Fork this repo
Clone the forked repository
cd to the directory where you cloned it
npm install to install dependencies
npm test to run the tests

Directions

This lab is designed to introduce you to the concept of writing code in a specific way, in order to make automated tests pass.

Once you have followed the setup instructions, look in the problems folder.

Each file in the problems folder contains a function that you must fill out to make the test pass. Above the function is a description of the function, the parameters it needs, and the return value.

Write your code in the function, then run npm test to check your work. When you're first starting out, all the tests will fail.

By default, npm test runs every test file, so you will have to scroll up to see all the output. See Reading the test output below for more info.

When writing your code, DO NOT change the name of the function, the filename, mess with the exports, or else the tests will not work.

The problem files are numbered, starting with 1, and we suggest doing them in that order.

Running Single Test Files

If you want to reduce the amount of output you get, you can test only a single file at a time.

Simply run npm test and then the name of the test file you want to run.

So to test the multiply problems, run:

npm test __tests__/multiply.test.js

Bonus Questions

Bonus questions are in the /bonus folder. To run the tests you can simply do npm run bonus

Submission requirements

When finished, commit your work.
Make a pull request on github.

If all your tests pass when you run npm test, then you should see a notice in the pull request that they all passed. If even one test fails on your computer, it will look like they all failed on github.

Reading the function description

Here is a sample description and function:

/**
 * Takes in two values and returns their average

 * @param {number} a - The first number
 * @param {number} b - The second number
 * @returns {number} - a number equal to the average of a and b
 */

function average() {

}

The first line describes, in a plain way, what the function should do.

The params contain the type and the suggested name of the parameters. In this case both are numbers, not strings, arrays, or objects. The first is named a and the second named b.

The returns line describes the type of value that should be returned from the function, and what it should be. So if it says number and you return a string then the test will fail.

Notice that the function is written without any parameters - you must add them in based on the description!

Reading the test output

When you run npm test you will see something like this:

 FAIL  __tests__/sum.test.js
  ● adds 1 + 2 to equal 3

    expect(received).toBe(expected) // Object.is equality

    Expected: 3
    Received: undefined

      2 | 
      3 | test('adds 1 + 2 to equal 3', () => {
    > 4 |   expect(sum(1,2)).toBe(3)
        |                    ^
      5 | })
      6 | 

      at Object.<anonymous> (__tests__/sum.test.js:4:20)

Test Suites: 2 failed, 1 passed, 3 total

The first line tells you which test file the message corresponds to. So if the file is named sum.test.js then it's probably referring to code you wrote in sum.js

The second line is the description of what the test is looking for.

The Expected and Received lines show what the test was hoping to get, and what it did get back. If it says it received something undefined you probably forgot to return inside the function.

Below that, the code shows what the test case does. It literally imports your function and tries to run it - so in this case, it runs sum(1, 2) and expects the function to return a 3.

Each test file may contain multiple tests! And each problem file may contain multiple functions, so make sure you read all the test output.

esayh/functions-lab