Unit Testing in TypeScript with Jasmine


Unit testing is a critical aspect of software development that helps ensure the correctness of your code. Jasmine is a popular testing framework for JavaScript and TypeScript that allows you to write and run tests for your code. In this guide, we'll explore unit testing in TypeScript using Jasmine, understand the core concepts, and provide sample code to demonstrate the process.

Why Unit Testing?

Unit testing offers several benefits:

  • Early Issue Detection: Unit tests catch bugs and issues early in the development process.
  • Code Quality: Writing tests encourages writing modular, maintainable, and well-structured code.
  • Regression Prevention: Tests act as a safety net, preventing regressions when making changes to the code.
  • Documentation: Tests serve as documentation, showing how code is supposed to work.

Setting Up Jasmine

Before you can write tests, you need to set up Jasmine. You can install it using npm:

npm install --save-dev jasmine

Initialize Jasmine:

npx jasmine init

Writing a Simple Test

Let's write a simple test for a TypeScript function. First, create a TypeScript file for your code and another one for the tests. For example:


// TypeScript code (Calculator.ts)
export function add(a: number, b: number): number {
return a + b;


// TypeScript code (CalculatorSpec.ts)
import { add } from './Calculator';
describe('Calculator', () => {
it('should add two numbers', () => {
const result = add(3, 5);

Compile your test file using the TypeScript compiler (tsc):

tsc CalculatorSpec.ts

Run the tests using Jasmine:

npx jasmine

You should see the test result in your console.


Unit testing with Jasmine in TypeScript is an essential practice for ensuring the quality and reliability of your code. By writing tests and automating the testing process, you can confidently develop and maintain software. As you become more familiar with Jasmine and unit testing, you'll be better equipped to produce high-quality code.