**Course Title:** Testing Frameworks: Principles and Practices **Section Title:** Unit Testing Fundamentals **Topic:** Write unit tests for a sample application using a chosen framework (e.g., Jest, JUnit).(Lab topic) **Overview** In this lab, you'll apply the concepts learned in previous topics to write unit tests for a sample application using Jest, a popular testing framework for JavaScript. You'll gain hands-on experience with Jest and see how it simplifies the process of writing, running, and maintaining unit tests. **Prerequisites** * Familiarity with JavaScript and Node.js * Understanding of unit testing concepts and principles * Basic knowledge of Jest (optional, but recommended) **Sample Application** For this lab, we'll use a simple calculator application written in JavaScript. The application has two functions: `add(num1, num2)` and `subtract(num1, num2)`. Our goal is to write unit tests for these functions using Jest. **Step 1: Set up Jest** If you haven't already, install Jest using npm by running the following command in your terminal: ```bash npm install --save-dev jest ``` Next, create a new file called `calculator.js` with the following code: ```javascript function add(num1, num2) { return num1 + num2; } function subtract(num1, num2) { return num1 - num2; } module.exports = { add, subtract }; ``` **Step 2: Write Unit Tests** Create a new file called `calculator.test.js` with the following code: ```javascript const { add, subtract } = require('./calculator'); describe('calculator', () => { it('adds two numbers', () => { expect(add(2, 2)).toBe(4); }); it('subtracts two numbers', () => { expect(subtract(4, 2)).toBe(2); }); it('adds two negative numbers', () => { expect(add(-2, -2)).toBe(-4); }); it('subtracts two negative numbers', () => { expect(subtract(-4, -2)).toBe(-2); }); }); ``` In this code: * We import the `add` and `subtract` functions from the `calculator.js` file. * We use the `describe` function to group related tests together. * We use the `it` function to define individual tests. * We use the `expect` function to assert that the output of the functions is correct. **Step 3: Run Unit Tests** Run the unit tests using the following command: ```bash jest ``` Jest will automatically discover and run the tests in the `calculator.test.js` file. You should see output indicating that all tests passed. **Tips and Variations** * Use the `beforeEach` and `afterEach` functions to set up and tear down test data. * Use the `describe` function to group related tests together. * Use the `it` function to define individual tests. * Use the `expect` function to assert that the output of the functions is correct. * Use the `.toBe()` matcher to assert that the output is equal to a specific value. * Use the `.not` matcher to assert that the output is not equal to a specific value. **Additional Resources** * Jest documentation: [https://jestjs.io/docs/en/getting-started](https://jestjs.io/docs/en/getting-started) * Jest API reference: [https://jestjs.io/docs/en/api](https://jestjs.io/docs/en/api) **Next Steps** In the next topic, we'll explore popular testing frameworks, including Jest, Mocha, JUnit, and NUnit. **Comment or Ask for Help** If you have any questions or need help with this lab, please leave a comment below. **Remember** * Writing unit tests is an essential part of software development. * Jest is a popular testing framework for JavaScript. * Use the `describe` function to group related tests together. * Use the `it` function to define individual tests. * Use the `expect` function to assert that the output of the functions is correct. Please let us know if you have any further questions or if there's anything else we can help you with.