Testing and code quality with Copilot

Software Development with GitHub Copilot

Thalia Barrera

AI Engineering Curriculum Manager, DataCamp

What you've learned

Code completions — suggestions as you type
Copilot Chat — ask questions, get explanations, and refactor code
Agent mode — autonomous, multi-step tasks
Custom tools — extending Copilot's capabilities

Now, let's apply it

nanobanana: half: A developer's journey shown as a path with three milestone icons representing testing, security, and performance, leading from a code editor toward a polished deployed application, flat vector illustration

Testing — catch bugs before they reach production
Security — spot vulnerabilities early
Performance — write code that scales

Copilot makes testing easier

nanobanana: half: An AI assistant generating test code on a developer's screen, showing green checkmarks next to test results, flat vector illustration

✔ Generate full test suites
💡 Catch edge cases
🤖 Handle boilerplate

The edge cases that slip through

def calculate_discount(price, discount_pct):
    discount = price * (discount_pct / 100)
    return price - discount

calculate_discount(50, 20)  # → 40.0 ✓

But what about...

Negative price
discount_pct > 100
Zero quantity order

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When to go deeper

nanobanana: half: A focused software developer at a laptop composing a message in an AI chat interface

Straightforward cases

/tests

Special cases

Write pytest unit tests for calculate_discount covering: negative price, discount > 100%, and empty item list. Use parametrize for edge cases.

Beyond unit tests

nanobanana: half: A testing pyramid with three stacked horizontal layers, the wide base labeled unit tests, the middle layer labeled integration tests, and the narrow top labeled end-to-end tests

Unit — /tests or a simple prompt
Integration — describe how components connect
End-to-end — use full codebase context

Integration tests

Attach each relevant file with #file:
Describe interaction and mocking strategy
Use /fixTestFailure if a test breaks

Write integration tests for the checkout flow. Use #file:cart.py and #file:payment.py. Mock the payment gateway and assert that order status updates correctly.

End-to-end tests

@workspace discovers relevant code automatically
Works well with Playwright and Cypress
Use #terminalLastCommand to debug failures

@workspace Write Playwright end-to-end tests for the user registration flow. Assert that the confirmation email is triggered.

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Let's practice!

Software Development with GitHub Copilot