Lab Instructions: Unit Testing

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Task 1: Add Jest as a devDependency

Open terminal. Make sure that it's pointing to jest-testing directory.
Install the jest npm package using the npm install command and the --save-dev flag.
Verify that the installation was completed successfully by opening the package.json file and confirming that the "devDependencies" entry lists jest similar to the following:

"devDependencies": {
    "jest": "^28.0.0"
}

Task 2: Update the test entry

In the package.json file, locate the "scripts" entry, and inside of it, update the test entry to jest.

Task 3: Code the timesTwo function

Open the timesTwo.js file and add a function named timesTwo. The function should take number as input and return the value 2 multiplied by the number. Export the timesTwo function as a module.

Task 4: Write the first test

Code a test call with the following arguments:

1. The description that reads: "returns the number times 2".

2. The second argument should expect the call to the timesTwo function, when passed the number 10, to be 20.

Task 5: Run the first test

With the terminal pointed at the jest-testing directory, run the test script using npm.

---

• timesTwo.test.js

    const timesTwo = require('./timesTwo');
  
    // Write the first test
    test('returns the number times 2', () => {
        expect(timesTwo(10)).toBe(20);
    });
  

• package.json

    {
      "name": "jest-testing",
      "version": "1.0.0",
      "description": "",
      "main": "index.js",
      "scripts": {
        "test": "jest"
      },
      "author": "",
      "license": "ISC",
      "devDependencies": {
        "jest": "^28.1.3"
      }
    }
  

• timesTwo.js

    // Task 1: Code the timesTwo function declaration
    function timesTwo(num){
        return num * 2;
    }
  
    // Task 2: Export the timesTwo function as a module
    module.exports = timesTwo;