Imagine remodeling your kitchen. It’s a big task, right? But when it’s done, you’ll have that perfect space where everything works just how you want it to. Contributing a new feature or plugin to a testing library is pretty much the same thing. You’re adding something new that, if done well, will make life easier for everyone who uses the library. Whether it’s a new matcher in Jest or a plugin for Mocha, your contribution can enhance how other developers write and run their tests. But just like remodeling a kitchen, it’s not something you want to rush into.

In this tutorial, we’ll walk you through how to plan, code, and submit a new feature or plugin for a testing framework. You’ll learn how to make sure you don’t break anything in the process, how to stay consistent with the project’s code style, and how to get feedback from the maintainers before submitting your pull request (because it’s a team effort, after all).

By the end of this tutorial, you’ll not only have written a feature or plugin, but you’ll have also experienced the entire process of contributing to an open-source project. That means planning, coding, getting feedback, and, most importantly, collaborating with others to make sure your contribution gets merged.

Step 1: Planning Your Feature or Plugin (And Why You Shouldn’t Dive in Headfirst)

One of the biggest mistakes you can make when contributing a new feature or plugin to a testing library is diving in without a plan. Sure, it’s tempting to just start coding, but taking a step back and thinking things through can save you hours of frustration (and potentially embarrassing mistakes).

Why Planning Matters:

When you’re working on an open-source project, it’s not just your codebase you’re dealing with. It’s a shared codebase that other people rely on. If you make changes without considering the bigger picture, you might end up breaking something or creating more work for others. By planning your feature or plugin in advance, you can ensure that your contribution adds value without introducing problems.

Steps to Plan Your Feature or Plugin:

1. Identify the Need: The first step in planning your feature is understanding why it’s needed. Maybe you’ve noticed a missing feature while using the testing library yourself, or maybe you’ve seen an issue raised by another user. Before you start coding, make sure that your feature or plugin solves a real problem.

2. Discuss It with the Community: Before you write any code, it’s a good idea to discuss your idea with the project maintainers or community. Open a new issue or join the project’s discussion forum to propose your idea. This step is important because the maintainers might already have plans for a similar feature, or they might be able to offer insights that you hadn’t considered.

   This step also helps to prevent duplicating work. There’s nothing worse than spending hours on a new feature only to find out someone else was already working on the same thing!

3. Define the Scope: Once you’ve discussed your idea with the community, it’s time to define the scope of your feature or plugin. What exactly are you going to build? What problem is it solving? What are the key functionalities you need to include? Defining the scope will help you stay focused and prevent feature creep (which is when a simple project grows into an overly complicated one).

4. Plan the Tests: Since you’re contributing to a testing framework, it’s important to think about how you’ll test your feature. What test cases will you write to ensure that your feature works as expected? If you’re building a plugin, what tests will verify that your plugin integrates properly with the framework? Planning your tests in advance ensures that your feature is robust and won’t break down the line.

Step 2: Writing the Code (Without Breaking Everything Else)

Now that you’ve planned your feature or plugin, it’s time to start coding. But here’s the catch: you can’t just write whatever you want and hope it works. You need to make sure that your code integrates seamlessly with the existing codebase and that it doesn’t break anything in the process.

Tips for Writing Your Feature or Plugin:

1. Start with a New Branch: Always, always, always create a new branch for your feature or plugin. Don’t work directly on the main or master branch. This way, if something goes wrong, you can easily switch back to a stable version of the code. Creating a new branch also makes it easier to submit a pull request later.

   git checkout -b feature/my-awesome-plugin
   

2. Stick to the Project’s Coding Standards: Every project has its own coding style, and it’s important to follow these standards when contributing new code. Most projects include a style guide or use a linter to enforce consistent formatting. Before you start coding, check the repository for a CONTRIBUTING.md file or a .eslintrc file that outlines the project’s rules for writing code.

   For example, some projects use 2 spaces for indentation, while others use 4. Some prefer camelCase for variable names, while others prefer snake_case. Whatever the rules are, stick to them – it’ll make your code easier to review and maintain.

3. Test Your Code as You Go: Don’t wait until the end to test your code. As you write each part of your feature or plugin, run the tests to make sure everything works. If you wait until the end to test, you might find that something broke earlier in the process, and it’ll be harder to figure out where the problem is.

4. Write Clean, Readable Code: Open-source projects are collaborative efforts, which means other people will need to read and understand your code. Write your code as if someone else will need to pick it up and work on it later (because they probably will). Avoid unnecessary complexity, use clear variable and function names, and add comments where appropriate.

Step 3: Keeping the Codebase Style Consistent (Linters and Style Guides Are Your Friends)

Consistency is key when working on an open-source project. The codebase should feel like it was written by one person, even though it’s actually been contributed to by many. This is where linters and style guides come in.

What’s a Linter?

A linter is a tool that checks your code for style and syntax errors. It helps ensure that your code follows the project’s rules for formatting and avoids common mistakes. Most JavaScript projects use ESLint as their linter, but there are other options as well.

Before you submit your feature or plugin, make sure to run the linter to check for any issues. If the project has a .eslintrc file, it means they’re using ESLint, and you can install the necessary dependencies by running:

npm install eslint

Then, run the linter with:

npm run lint

The linter will highlight any issues with your code, such as inconsistent indentation, unused variables, or missing semicolons. Fix these issues before submitting your pull request.

Following the Style Guide:

Many projects also include a style guide that outlines the conventions for writing code. The style guide might cover things like how to name variables, when to use comments, and how to structure functions. Following the style guide is important because it keeps the codebase consistent and makes it easier for others to read your code.

Step 4: Writing Documentation for Your New Feature (Yes, You Have to Do This Too!)

Ah, documentation. It’s not the most glamorous part of coding, but it’s arguably one of the most important. If you contribute a new feature or plugin without documenting how to use it, other developers won’t know how to take advantage of your work. So, yes, writing documentation is a must.

What to Include in Your Documentation:

1. Description of the Feature or Plugin: Start by explaining what your feature or plugin does. What problem does it solve? How does it work? Keep it simple and to the point – the goal is to help other developers understand the value of your contribution.

2. Installation Instructions (If Necessary): If your plugin requires installation or setup, make sure to include clear instructions. For example, if your plugin is for Mocha, you might include a command like:

   npm install mocha-my-plugin --save-dev
   

3. Usage Examples: The best way to show how your feature or plugin works is by including usage examples. For example, if you’ve added a new matcher to Jest, show how to use it in a test:

   test('is even number', () => {
     expect(4).toBeEven();
   });
   

4. API Documentation (If Applicable): If your feature or plugin includes a new API, document each method or function, including any parameters and return values. Make sure to explain what each part of the API does and when it should be used.

Step 5: Getting Feedback from the Project Maintainers Before Submitting a Pull Request

Before you submit your pull request, it’s a good idea to get some early feedback from the project maintainers. This can save you a lot of time and effort in the long run, as they might point out potential issues or suggest improvements before you finalize your code.

Here’s how to do it:

1. Open a Draft Pull Request: Instead of waiting until your feature is completely finished, open a draft pull request early in the process. This lets the maintainers know that you’re working on something, and they can start reviewing your code while you’re still making changes.

2. Ask for Feedback: In your draft pull request, explain that you’re still working on the feature and ask for feedback. Be open to suggestions – remember, the maintainers want to help you make your contribution as good as it can be.

3. Iterate Based on Feedback: Once you’ve received feedback, make any necessary changes to your code. This might involve fixing bugs, improving the code’s readability, or adding additional tests.

Writing and Submitting Your Feature or Plugin

Now that you’ve learned how to plan, code, and document a new feature or plugin, it’s time to put that knowledge into practice. Choose a testing library you want to contribute to, plan a small feature or plugin, and start writing the code.

Once you’ve written your feature, follow the steps outlined above to submit a pull request. Remember to get feedback from the maintainers before finalizing your code, and make sure to document everything so that others can easily understand and use your contribution.

By the end of this tutorial, you’ll have experienced the entire process of contributing a new feature or plugin to an open-source project. You’ve written code, collaborated with the community, and made the software world a little bit better. Well done!