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🤖 GitHub Copilot
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How GitHub Copilot Can Write Unit Tests for Your Code

A step-by-step beginner guide that shows you how to ask Copilot to generate test snippets, so you can automatically cover new functions with confidence.

6 min read·June 28, 2026

This guide was written by AI. It passed automated fact and quality checks, and our editor spot-checks published guides every day.

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By the end of this guide, you’ll be able to type a simple comment and let Copilot spin up a ready-to-run unit test for any function you create. A unit test is like a tiny, automatic quality check for a small piece of your code, ensuring it works as expected. This guide is aimed at anyone who writes a little bit of code – no testing specialist required.

💡 Tip: tap a step’s number when you finish it — a green tick appears and your browser remembers how far you got.

✅ Before you start
  • GitHub account – you'll need to sign in so Copilot can link to your editor.
  • Visual Studio Code (VS Code) – this is a free, cross-platform program where you write code. It's often called a 'code editor'.
  • GitHub Copilot subscription or free trial – the first 30 days are free for most users. A paid plan may be required for unlimited suggestions after this period.
  • Internet connection – Copilot contacts GitHub’s servers to generate suggestions, so you'll need to be online.
  • Node.js and npm (for JavaScript) – If you plan to test JavaScript code, you'll need Node.js (a program that runs JavaScript outside of a web browser) and its package manager, npm (a tool to install extra software 'packages' for Node.js). You can download them from the official Node.js website.
  • Rough time – about 10-15 minutes from start to a passing test.

If all these items are ready, you’re good to go.

1
Step 1 of 5

Install and enable Copilot in VS Code

Open Visual Studio Code (VS Code) on your computer. Look for the Extensions view, which is usually a square-shaped icon made of four smaller squares in the left-hand toolbar (it looks a bit like puzzle pieces). Click this icon. In the search box that appears, type "GitHub Copilot" and click the Install button next to the official GitHub Copilot entry. After the download finishes, a pop-up might ask you to sign in to GitHub. Click the link, log in with your GitHub account, and grant the permission the extension requests. When the sign-in completes, you'll see a tiny Copilot logo in the lower-right status bar (this is the strip at the bottom that shows things like file name and line number). Click that icon and toggle the switch so it reads "Enabled".

💬 ExampleIf a sign-in pop-up doesn't appear, look for a notification bell icon in the bottom-right status bar or check the Output panel (View > Output) for prompts.
✅ You'll know it worked when

the Copilot icon in the status bar turns blue and, if you hover your mouse over it, the tooltip reads "GitHub Copilot enabled".

Next step ↓
GitHub CopilotInstall
✏️ Sketch — your screen may look a little different
2
Step 2 of 5

Write the function you want to protect

Create a new file for the programming language you’re working with. For example, you might choose utils.py for Python or utils.js for JavaScript. To do this, go to the top menu, select File > New File, then save the file with the appropriate extension (e.g., .py or .js). In the main editor area, type a simple function; keep it short for this example so Copilot can see the whole definition clearly. A function is a block of code designed to perform a specific task.

💬 Example(Python):
def add(a: int, b: int) -> int:
 return a + b
💬 Example(JavaScript):
function add(a, b) {
 return a + b;
}

Click it and select the correct language (e.g., "Python" or "JavaScript").

✅ You'll know it worked when

the function appears with proper syntax coloring (keywords in blue, strings in green, etc.) and no red squiggles indicating syntax errors.

🔄 If it looks different

If your code doesn't get proper coloring, check the language mode in the bottom-right status bar of VS Code (it might say "Plain Text").

Next step ↓
GitHub CopilotFile > New File
✏️ Sketch — your screen may look a little different
3
Step 3 of 5

Prompt Copilot to generate a unit test

Place your text cursor on a brand-new, empty line directly below the function you just wrote. Type a comment that tells Copilot what you need. A comment is a line of text in code that is ignored by the computer but helps humans understand what's happening. For Python, use # Write a unit test for add(); for JavaScript, use // Write a Jest test for add(). After typing your comment, press Enter. Copilot will instantly show a greyed-out suggestion that looks like code, but isn't yet part of your file. This is Copilot offering to help!

💬 Example(JavaScript comment): `// Write a Jest test for add()`

Sometimes Copilot takes a second to think. Ensure Copilot is enabled (blue icon in status bar). If you still see nothing, try rephrasing your comment slightly, or saving the file (Ctrl+S). If the suggestion looks correct, press Tab to accept it; otherwise, press Esc to dismiss it and try a slightly different comment.

✅ You'll know it worked when

a block of test code appears in the editor as a gray suggestion.

🔄 If it looks different

If no suggestion appears, wait a moment.

Next step ↓
GitHub CopilotEnter
✏️ Sketch — your screen may look a little different
4
Step 4 of 5

Run the test and see it pass

Now that you have your test code, it's time to run it. Open VS Code’s integrated terminal by selecting View > Terminal from the top menu (or press Ctrl+ on Windows/Linux, orCmd+`` on Mac). The terminal is a command-line interface where you can type commands for your computer. In the terminal, type the command that runs the test file you just generated. For Python, if your test file is namedtest_utils.py, run: python -m unittest test_utils.py. For JavaScript with Jest (a popular *test runner* or tool for running JavaScript tests), type npm test`.

💬 Example(Python): `python -m unittest test_utils.py`

In the terminal, run npm install --save-dev jest (which means "install Jest and save it as a development dependency"), then retry npm test. For Python, if unittest isn't found, ensure Python is correctly installed and added to your system's PATH.

✅ You'll know it worked when

the terminal prints a line that says OK (or shows only dots without a "FAIL" label), indicating all tests passed.

🔄 If it looks different

If npm test doesn't work for JavaScript, it's probably because Jest isn't installed in your project yet.

Next step ↓
GitHub Copilotpython -m unittesttestutils.py
✏️ Sketch — your screen may look a little different
5
Step 5 of 5

Tweak or add more test cases

Take a look at the test file Copilot produced. You'll likely see a test method or test case like test_positive_numbers inside a class (for Python) or a test() block (for JavaScript). To cover extra situations for your add function (for example, handling zero values, negative numbers, or very large numbers), copy an existing test method or block, paste it below, and change the input numbers and the expected result. A test case is a specific scenario you want to check. Save the file (Ctrl+S), then rerun the command from Step 4 in the terminal to confirm the new cases also pass.

💬 Example(add a zero case in Python):
def test_zero(self):
 self.assertEqual(add(0, 0), 0)

The test runner only sees the saved version of your code. Copilot can draft tests, but it can't run them or interpret the results for you.

✅ You'll know it worked when

the terminal again prints OK (or all green dots) and the total number of tests reported matches the total number of test methods you now have in your file.

🔄 If it looks different

If you add new tests and the terminal still says the same number of tests passed, ensure you saved the file after making changes (Ctrl+S).

Tweak or add more test cases
⚠️ Common mistakes
  • Forgetting to save your function before prompting Copilot. Copilot only reads the saved file, so unsaved changes won’t be considered. Fix: Press Ctrl+S after writing your function and before typing the comment for Copilot.
  • Running the JavaScript test without Jest installed. Python’s unittest is built-in, but JavaScript needs Jest (or another test runner) installed first. Fix: Run npm install --save-dev jest in your terminal, then retry the npm test command.
  • Accepting a test that imports a library you don’t have. Copilot sometimes suggests import pytest for Python even if you haven’t installed it. Fix: Either install the missing library (e.g., pip install pytest for Python) or edit the import line to use the built-in unittest module instead.
🚀 Try it now

Open VS Code, create a new file called add.py, paste the add function from Step 2, add the comment # Write a unit test for add(), hit Enter, then press Tab to accept Copilot’s suggestion. You’ll have a complete test file ready to run in under two minutes. Happy testing!

🎯 Next guideSafely Rename a Batch of Photos with a GitHub Copilot ScriptUse Copilot in VS Code to generate a small Python script, test it on copies, then rename your real photos in one click.

❓ Quick questions

How long does this take?

About 6 minutes — the guide has 5 steps, and you can tick each one off as you go.

Which tool do I need?

This guide uses GitHub Copilot — but the approach works very similarly in other AI assistants.

Do I need to prepare anything?
  • GitHub account – you'll need to sign in so Copilot can link to your editor.
  • Visual Studio Code (VS Code) – this is a free, cross-platform program where you write code. It's often called a 'code editor'.
  • GitHub Copilot subscription or free trial – the first 30 days are free for most users. A paid plan may be required for unlimited suggestions after this period.
  • Internet connection – Copilot contacts GitHub’s servers to generate suggestions, so you'll need to be online.
  • Node.js and npm (for JavaScript) – If you plan to test JavaScript code, you'll need Node.js (a program that runs JavaScript outside of a web browser) and its package manager, npm (a tool to install extra software 'packages' for Node.js). You can download them from the official Node.js website.
  • Rough time – about 10-15 minutes from start to a passing test.

If all these items are ready, you’re good to go.

What mistakes should I avoid?
  • Forgetting to save your function before prompting Copilot. Copilot only reads the saved file, so unsaved changes won’t be considered. Fix: Press Ctrl+S after writing your function and before typing the comment for Copilot.
  • Running the JavaScript test without Jest installed. Python’s unittest is built-in, but JavaScript needs Jest (or another test runner) installed first. Fix: Run npm install --save-dev jest in your terminal, then retry the npm test command.
  • Accepting a test that imports a library you don’t have. Copilot sometimes suggests import pytest for Python even if you haven’t installed it. Fix: Either install the missing library (e.g., pip install pytest for Python) or edit the import line to use the built-in unittest module instead.

Keep reading

📘 Generate Basic, Reusable Code Snippets with GitHub Copilot Learn how GitHub Copilot can write starter code for you — from date formatting to simple API calls — even if you're not a full-time developer. 📘 Add helpful comments to your code with GitHub Copilot – beginner guide A friendly step‑by‑step walkthrough that shows anyone how to get GitHub Copilot to write plain‑language comments for any line of code 📘 Safely Rename a Batch of Photos with a GitHub Copilot Script Use Copilot in VS Code to generate a small Python script, test it on copies, then rename your real photos in one click. 📘 Getting started with GitHub Copilot: a beginner's guide Learn how to let AI write code for you safely, right inside your editor, so you can finish small projects faster. 📘 Build a Simple Household Budget Calculator with GitHub Copilot Write a small calculator that adds your monthly expenses — Copilot helps you write the code, line by line. 📘 How to Ask GitHub Copilot to Explain a Confusing Error Message A beginner's way to turn cryptic red text into a clear, friendly to-do list
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