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Valentina Gomez
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How To Setup TypeScript Testing?


Testing TypeScript code is crucial for reliability and stability, whether you're new to TypeScript testing or looking to enhance your testing experience. This blog post will explore the fundamentals of TypeScript testing, from setup to execution, and provide insights into advanced testing techniques.

What is TypeScript Testing?

TypeScript testing ensures your production code is reliable and functions as intended. Within Software Development, it includes writing tests, specifically unit tests, to assess single, isolated pieces of codes—a critical step for identifying issues early on.

TS further has several testing frameworks for devs and teams to run efficient tests, like Jest, Mocha, and the browser-oriented Karma. These frameworks often require configuration files to set up development dependencies, set coverage metrics, and specify the resolver for imports to handle external dependencies properly.

Tests are typically stored in a project folder, with a common practice being to create a dedicated tests or __tests__ directory within the src folder. For convenience, most frameworks come with a command line interface that displays test results and can run tests in parallel, speeding up the testing process.

Unit Tests vs Testing Frameworks

Unit tests are the backbone of software reliability, meticulously scrutinizing individual code blocks to catch glitches before they spiral. These functional tests are akin to quality checkpoints, ensuring each code unit performs its task flawlessly within the source code universe.

Now, envision a toolkit where testing frameworks enter the stage. They're the architects of the testing realm, employing seamless strategies that developers use to automate and run unit tests. Community favorites include Jest for its zero-configuration option and Mocha for its flexibility. Each one demands a simple configuration file and an unassuming architect’s plan to guide the development dependencies and manage the external elements.

But what's a builder without tools? Assertion libraries act as hammers and nails, setting the foundation for how tests and expected outcomes should be expressed.

The modern development toolbox wouldn't be complete without a package manager, such as npm or Yarn, to elegantly orchestrate these essentials into the src folder, turning testing into an orchestrated symphony of checks and balances.

TypeScript Type Tests

Testing in TypeScript comes with a special encore: type tests. TypeScript is particular about types—the roles that each variable and parameter plays. These tests scrutinize whether the type definitions within your code are in harmony. It goes beyond the script of your production code to ensure a flawless performance under the type-checking spotlight.

Type tests don't need a standing set. During compilation, they operate in the background, assessing whether your interfaces and types are set up correctly in every scene—er, source file. Think of it as an over-the-shoulder glance from the director, ensuring everyone knows their lines before going live.

TypeScript Additional Tests

Like a theater production, which needs more than just lead actors to shine, your software testing lineup craves a diverse cast. Profiling tests detect and pinpoint areas in software where its performance is slow. On the other hand, cloud-based tests utilize cloud setups to run tests in different environments to ensure the software's functionality and stability.

These additional tests can provide insights into your application's performance under different conditions and workloads. They are essential checks that guarantee functionality and optimize the User Experience.

TypeScript Integration Tests

If unit tests are solo performances, integration tests are the grand ensemble. Here, the entire cast comes together to rehearse full scenes, ensuring that different units of your source code interact perfectly on stage. They check data flow across modules, confirm that external dependencies get their cues right, and make sure the entire application runs harmoniously.

Integration tests are crucial to catch blunders that might spoil the entire production before the audience—your users—ever see it.

Why is TypeScript Testing Important?

TypeScript testing plays a crucial role in the development process by enhancing code quality and reducing the risk of introducing defects. Here are some key reasons why TypeScript testing is essential:

 Code Quality: Writing tests force you to think critically about your code and its behavior. It encourages you to write clean and modular code, improving code quality and maintainability.
 Bug Detection: By writing tests, you can catch bugs and issues before they make their way into production. That helps you identify and fix potential problems early on, saving time and effort in the long run.
 Regression Prevention: As your codebase grows and evolves, new features and changes can inadvertently introduce regressions. By running tests regularly, you can catch these regressions early and prevent them from affecting your application's functionality.
 Refactoring Confidence: Refactoring is integral to Software Development but can introduce new bugs if not done carefully. Having comprehensive tests in place gives you the confidence to refactor your code while ensuring that existing functionality remains intact.

How To Set Up TypeScript Testing Environments?

Now that you understand the importance of TypeScript testing, let's dive into setting up your environment to start writing tests. First, you'll need a few essential tools and software before you can write tests for your TypeScript code. Here are some of the key components you'll need to set up your testing environment.

Test Runner. A test runner is a tool that executes your tests and provides feedback on their results. Several popular test runners are available for TypeScript, such as Jest, Mocha, and Karma.
Assertion Library. An assertion library allows you to define expectations and assert that certain conditions are met during your tests. Popular choices include Chai and Jasmine.
 Mocking Framework. You may need to simulate certain behaviors or dependencies when writing tests. A mocking framework, such as Sinon or Jest's built-in mocking capabilities, can help you create a mock activity environment and stub functions.

TypeScript Testing Configuration

In constructing tidy, testable TypeScript code, the blueprint to success often lies in the proper configuration and expert management of dependencies. Like how skilled chefs meticulously organize their kitchens for a seamless cooking experience, TypeScript testing requires a methodically arranged environment. Let's break down this gourmet setup into three key ingredients: the configuration file, development dependencies, and external dependencies.

TypeScript Testing Configuration Files

The configuration file acts as your personalized recipe. These are the instructions laying out precisely what ingredients you need and how your testing environment should behave. This file determines the game's rules, telling your code editor which testing frameworks to employ and setting the tone for executing tests. It's less about complex coding magic and more about setting preferences that enable your code to be tested consistently.

TypeScript Testing Development Dependencies

Beyond the basics, your project folder has a special corner called 'development dependencies.' These are the assortments of tools that assist in testing your production code without appearing in the final act – your deployed application. They include the Jest or Mocha testing frameworks, the assertions library for test validations, and perhaps a resolver for imports to keep your code clean and organized.

 Jest/Mocha (Unit Testing Frameworks)
 Chai (Assertion Library)
 Typescript (Language Superset)
 ts-node (Execution in Node.js)

TypeScript Testing External Dependencies

Last in the pantry are the external dependencies. Unlike their development counterparts, these ingredients become part of your application's performance, which is essential during testing and in the live environment. Examples include the libraries your application uses to fetch data, handle dates, or anything else it needs to function in the harsh reality of production.

Remember, a well-configured testing environment with thoughtfully chosen dependencies is like a well-oiled machine; it makes the process of writing, running, and passing tests as smooth as silk. With the right setup in your project's src folder, those unit tests become a powerful ensemble in the symphony of Software Development.

How to Organize a TypeScript Project?

Organizing your TypeScript project is akin to being a director who knows precisely where every prop goes and what each cast member does. A well-organized project folder is your backstage; keeping it orderly ensures that rehearsals lead to standing ovations. Here's how to bring order to your project and lay the foundation for a testing masterpiece.

Folder/File Purpose
src/ Houses the main source files.
tests/ Contains all the test scripts.
node_modules/ Stores all external dependencies.
src/ Houses the main source files.
package.json Tracks project metadata and dependencies.
tsconfig.json The configuration file for TypeScript.
coverage Holds code coverage reports.

This layout keeps your scripts organized and easily directs any new contributors backstage. Here’s a breakdown of the tips to keep order in your code.

TypeScript Project Source Code and Unit of Code

The heart of your TypeScript project beats within the src/ folder. Here, every unit of code—from functions to classes—gets its own spotlight. Each file is a script, and every function or class is a character contributing to your application's story. For seamless production, ensure each code unit has a well-defined role and interacts cleanly with others. It's like ensuring every actor knows their lines and marks, preventing on-stage collisions, and ensuring a smooth narrative flow.

TypeScript Project Code Editor

The code editor is your trusty assistant director. It keeps the script in order and alerts you to any fluffed lines or missteps in rehearsals. A good code editor, like Visual Studio Code, assists with syntax highlighting, code formatting, and IntelliSense (code suggestions). Embracing a code editor with TypeScript support integrates the rehearsal and rewriting process, making your job smoother as you refine your application.

TypeScript Project Package Manager

Finally, let's talk about the package manager. Tools like npm or yarn manage all the bits and pieces required to put on your show. They track your development dependencies (like your testing frameworks) and ensure your external dependencies are current. To use a package manager effectively, install it globally via your terminal, initialize it in your project folder to create a package.json file, and add dependencies with commands like npm install <package>. Think of the Package Manager as the person who keeps track of all the props, ensuring that nothing essential for the performance is missing when the curtain rises.

How to Code a TypeScript Test?

Now that you have a solid understanding of TypeScript testing and the different types of tests, it's time to dive into writing your first test.

1. TypeScript Test File

First, create a new file for your test. Conventionally, test files are placed in a separate directory named "tests" or "spec" alongside your source code files. For example, if you have a file called "calculator.ts" containing your calculator module, you might create a test file named "calculator.test.ts." Make sure to import the necessary dependencies for testing, such as your test runner and assertion library. Additionally, import the module or function you want to test from your source code.

2. TypeScript Test Cases

You can start writing test cases once your test file is set up. A test case typically consists of a single function that contains one or more assertions to verify the behavior of your code. Each test case should focus on your code's specific aspect or functionality and target a particular input or scenario. Keep your test cases small and focused, making it easier to identify the cause of any failures and maintain the tests in the future.

3. TypeScript Test Debugging

After you've written your test cases, it's time to run and debug your tests. Most test runners provide a command-line or graphical interface for running tests. Depending on your setup, you may need to configure the test runner to find and execute your test files. Pay attention to the test results and any failures or errors when running your tests. Test runners typically provide detailed information about failed assertions, allowing you to identify the issue's source quickly.

Additionally, you can use debugging tools provided by your test runner or Integrated Development Environment (IDE) to step through your tests and inspect variables at runtime. Debugging your tests can help you understand the flow of your code and identify any issues that may not be apparent in the test results.


TypeScript testing is an ongoing process that requires continuous learning and improvement. By investing time and effort into writing comprehensive and reliable tests, you can ensure the stability and success of your TypeScript applications.