How GitHub Copilot Can Write Unit Tests for Your Code

Install and enable Copilot in VS Code

1. Open VS Code.
2. In the left‑hand Extensions pane (the square‑icon view), search for “GitHub Copilot”. Click Install.
3. After installation, a pop‑up will ask you to sign in to GitHub – follow the link, log in, and authorise the extension.
4. When the sign‑in is complete, you’ll see a small Copilot icon in the status bar (bottom‑right). Click it and toggle the switch to Enabled.

Write the function you want to protect

1. Create a new file (e.g., utils.py for Python or utils.js for JavaScript).
2. Write a simple function. For illustration, let’s add a function that returns the sum of two numbers.

def add(a: int, b: int) -> int:
    return a + b

function add(a, b) {
    return a + b;
}

Why? Copilot learns from the code right in front of it; the clearer the function, the better the test suggestion.

Prompt Copilot to generate a unit test

1. Place the cursor on a new line below the function.
2. Type a comment that tells Copilot what you need, such as # Write a unit test for add() (Python) or // Write a Jest test for add() (JavaScript).
3. Press Enter. Copilot will instantly suggest a test block. The suggestion appears as greyed‑out text; press Tab to accept it, or Esc to reject and try another prompt.

import unittest
from utils import add

class TestAdd(unittest.TestCase):
    def test_positive_numbers(self):
        self.assertEqual(add(2, 3), 5)

    def test_negative_numbers(self):
        self.assertEqual(add(-1, -4), -5)

if __name__ == '__main__':
    unittest.main()

What’s happening? A unit test is a tiny piece of code that checks one small part of your program – like a quality‑control checkpoint for a single function.

Run the test and see it pass

1. Open a terminal inside VS Code (Ctrl+ `).
2. For Python, run: python -m unittest utils_test.py (or whatever you named the test file).
   For JavaScript with Jest, run: npm test (make sure Jest is installed; you can add it with npm i -D jest).
3. If everything is green, Copilot’s suggestion worked! If a test fails, read the error message – it will tell you which expectation didn’t match.

..
----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK

Tweak or add more test cases

1. Look at the generated test file. You can add extra scenarios (e.g., testing with zero or large numbers) by copying an existing test method and changing the inputs.
2. Save the file and re‑run the command from Step 4 to confirm the new cases also pass.

def test_zero(self):
    self.assertEqual(add(0, 0), 0)

Why tweak? Copilot gives a solid starter, but you may need edge‑case coverage that matches your real‑world data.