Skip to main content

Use Case 2: "We need better test coverage"

Scenario: Your tech lead says: "Our API test coverage is at 45%. We need to get it above 80% before the release."

Time: ~20 minutes

Copilot Features: Prompt Files, Self-Healing

Your Challenge: Systematically improve test coverage across all API routes.

Step 1: Use a Reusable Prompt File​

Manually prompting for test coverage improvements can work. However, it also means that the process may be inconsistent between developers and you never learn from mistakes. Instead, (have Copilot) create a documented prompt file checked into your repository. Utilize this and enhance it over time based on responses where Copilot struggled. Here we have provided a starting point (well, Copilot has)!

  1. If you haven't already, click the + button in the Copilot Chat panel to clear your history. This is a best practice when switching between use cases or activities to avoid sending unrelated context.
  2. Review .github/prompts/demo-unit-test-coverage.prompt.md
  3. Notice it defines:
    • Objective and routes to focus on
    • Testing patterns to follow (examples)
    • Success Criteria
    • Links to relevant documentation
  4. Notice the prompt does not say the percentage desired is greater than 80%. If that was important it could be added here.

Step 2: Execute the Prompt​

  1. Switch to Agent mode, select the Claude Sonnet 4.6 model
  2. Run the prompt:
    • Option A: Click the play button when the prompt file is open
    • Option B: Type /demo-unit-test-coverage in chat. The prompt name automatically becomes a slash command.

Step 3: Agent Self-Heals Failures​

Agent will:

  • Analyze current coverage
  • Generate new test cases for product and supplier routes
  • Run tests automatically
  • Fix any failures
  • Re-run until tests pass

Important: Press q when coverage report shows to let agent continue. Otherwise it will wait indefinitely.

Step 4: Verify Results Yourself​

make test

Review the coverage report - it should be significantly improved.

What You Learned​

✅ Prompt Files - Reusable, documented workflows
✅ Iteration - Agent iterates to fix failing tests automatically
✅ CodeQL Integration - Agent runs security scans after changes

Time Investment: 20 minutes
Value: Comprehensive test suite that would take days to write manually

Next Steps​

Continue to Consistent Standards to learn how to enforce team standards with Copilot.