What's the best way to test front-end components?

To build a front end of bigger or enterprise level application, you might need to write some code which would be repeated multiple times. For example, a contact us form or a wrapper div containing share on social media links inside. Since we need to write it again and again, we may create a block of code with it's own markup, style and interactivity which you don't need to write again and again. These can be written in many ways including React, Vue, angular or even in browser's native Web components. It will reduce clutter in the code and will help you to organise the code better.

The frontend ecosystem also has a composition of patterns that are used alongside components, also known as patterns, for example: the container pattern, the dumb component pattern, the smart component pattern, the high order components pattern. Each ecosystem such as reactjs, angular, vuejs share those patterns, but, each one of them have their own as well. Following such patterns might lead to cohesive components, and, they can also improve testability.

Front-end components are reusable pieces of code that can be used to build user interfaces. They are typically written in HTML, CSS, and JavaScript, and they can be used to create anything from simple buttons to complex menus and forms. Reusability: Components can be reused throughout your web application, which can save you a lot of time and effort. Maintainability: Components make your code more maintainable, as you can easily update and replace individual components without affecting the rest of your codebase. Scalability: Components make your code more scalable, as you can easily add new components to your web application as it grows. Consistency: Components help to ensure that your web application has a consistent look and feel.

To efficiently test front-end components: - Unit Testing: Test individual components in isolation using tools like Jest or Mocha. - Integration Testing: Assess how components interact within the application. - End-to-End (E2E) Testing: Use tools like Cypress or Selenium to simulate user workflows. - Snapshot Testing: Capture and compare component snapshots for visual consistency. - Accessibility Testing: Ensure components are usable for all users with tools like Axe. - Performance Testing: Identify and optimize component speed and efficiency. - Cross-Browser Testing: Test on various browsers for compatibility. - CI/CD Automation: Integrate testing into your development pipeline for continuous feedback.

Front-end components are like piecing together intricate Lego blocks. Each digital brick represents a reusable front-end component, like buttons, menus, or cards, forming the core of what users see on websites and apps. These components save developers time by sparing them from building everything from scratch. They also bring order and efficiency, making updates and fixes a breeze. Just like Lego bricks, front-end components are the building blocks of digital creations - essential, reusable, and crucial for crafting amazing digital experiences!

Testing front-end also gives an idea of how efficient component you have built. If you are not able to write test cases which can test your component easily, that's a reality check for your component, and the same has to be improved in no time.

Well testing is equally important as building, because that's how we find out whether our software is up to the mark for the scale we're building it or not, if you don't test it throughly, you don't know what're it's limitations, when does it break? And no one wants to break in production. haha.

Testing in the frontend is trickier and there external factors that it has to support make it much more challenging. Here I will enumerate a few: 1. The frontend has an added complexity from the execution model that it is in (the brower) 2. The intention of developing frontend code is to have an end user interacting with it, not only in a behaviour perspective but also in a visual one, in other words, how things are rendered and if they look as they supposed to be looking is also important. 3. Given the javascript ecosystem, building up the environment to test an application usually requires extras steps, for example, setting up the dom correctly, making sure to use test-doubles to avoid interacting with global etc.

Ensuring the reliability and reusability of front-end components is crucial; testing them is an essential step towards achieving this goal. As separate components, they should be free of errors and designed with extensibility in mind in order to meet the requirements. If proper testing, preferably automated, is not conducted, it becomes easy to introduce bugs or make changes that can cause integrity failures. Therefore, proper testing is vital to ensure the stability and functionality of front-end components.

It is ideal to combine unit, integration, and accessibility tests. This can be achieved for frontend components by using tools like Storybook and testing frameworks together. Testing frameworks can help implement most of the unit and integration tests, while Storybook can render components in isolation or composition with provided state.

Unit Testing: Use unit testing frameworks like Jest (for JavaScript) or XCTest (for Swift) to test individual components, functions, or methods in isolation. This helps catch small bugs early. Integration Testing: Test how different components work together. Tools like Cypress, Selenium, or Puppeteer are great for simulating user interactions and checking if components integrate smoothly. End-to-End Testing: Perform end-to-end tests to simulate real user scenarios. Tools like Selenium, Playwright, or Cypress can help you automate user interactions across your application. Snapshot Testing: Use tools like Jest Snapshot Testing to capture and compare component snapshots. This is especially useful for ensuring UI consistency across updates.

While choosing tools in your front-end components, one should ideally be looking for something which satisfies the team needs. Choosing something blindly will not be a good decision to make. For instance, let's say, you want to do unit testing only for your component and need a testing library. In libraries like ReactJS, Jest comes by default, and it is actually good for your unit testing. Installing a third-party library will not be a good idea in this case, as it involves unnecessary space consumptions, which eventually impacts your app size.

While writing test cases, it is a good idea to keep in mind to test those things which the user is going to be interacting with on your web app. This will make sure that you are writing quality test cases, and also your web app's functionalities are to the point as per the expectations of the delivery. This will help you avoid making your test cases look bulky and redundant.

Follow the real meaning of components, which is a component should only do one thing and should be re usable. That's how it's easier to test and maintain it. Many times we create a component for some purpose and then add other things also maybe because of laziness to create a new one but it makes tough to track and test the changes and other things.

When feasible for "dumb" components, consider using Storybook to maintain an interactive documentation setup. It helps a lot in verifying and testing components independent of their context.

In my experience, testing front-end components is essential for ensuring quality and reliability. As projects grow, the challenges of complexity become apparent. To address this, mastering unit, integration, and end-to-end testing is crucial. However, it's not just about the tools; organizing, writing, and maintaining good test cases is equally important. Optimizing performance, security testing, and visual testing are also key. With patience and dedication to front-end testing, we can create better web experiences and tackle challenges as our projects expand.

Creating highly modular front-end components is crucial for widespread use across various layouts. Modular components are self-contained, promoting reusability. They ensure design consistency, scalability, and easier maintenance. Developers can efficiently customize these components, and they encourage clean code organization. Collaboration is simplified, and testing becomes more manageable due to well-defined inputs and outputs. Overall, modular components streamline development, making it more efficient and adaptable for different projects and layouts.