Overview

Duration	35 minutes
Level	Intermediate
Prerequisites	Lab 00, Lab 01, Lab 02

Learning Objectives

By the end of this lab, you will be able to:

• Run test coverage and understand the coverage gap in the sample app
• Run the code-quality-detector to find quality issues including coverage, complexity, and maintainability
• Use the test-generator to create unit tests for uncovered code
• Observe coverage improvement after applying generated tests

Exercises

Exercise 5.1: Measure Current Coverage

Before running any agents, establish a baseline by measuring the current test coverage.

1. Open a terminal in VS Code (Ctrl+ ) and navigate to the sample app:

   cd sample-app
   

2. Run the test suite with coverage reporting:

   npm test -- --coverage
   

3. Review the coverage output. You should see coverage around 5% because only a placeholder test exists in __tests__/placeholder.test.ts.
4. Note the specific files and functions with 0% coverage. These are the targets for later exercises.

Exercise 5.2: Code Quality Detection

Use the Code Quality Detector agent to get a comprehensive quality analysis.

1. Open the Copilot Chat panel (Ctrl+Shift+I).

2. Type the following prompt:

   @code-quality-detector Analyze sample-app/ for code quality issues including coverage, complexity, and maintainability
   

3. Review the findings. The detector should identify issues such as:

   Finding	Category	File
   Test coverage below 80% threshold	Coverage	Project-wide
   High cyclomatic complexity	Complexity	sample-app/src/lib/utils.ts
   Use of any type annotations	Type Safety	Multiple files
   Code duplication in utility functions	Maintainability	sample-app/src/lib/
   Missing error handling	Reliability	sample-app/src/lib/db.ts

4. Note which findings the detector flags as highest priority. Low coverage and type safety issues are common starting points for improvement.

Exercise 5.3: Generate Tests

Use the Test Generator agent to create unit tests for one of the uncovered files.

1. In Copilot Chat, type:

   @test-generator Generate unit tests for sample-app/src/lib/utils.ts to improve coverage
   

2. Review the generated test file. The agent should produce tests that cover:

   • Each exported function in utils.ts
   • Edge cases (null inputs, empty strings, boundary values)
   • Expected return values for common inputs

3. Examine the test structure. The generated tests should use Jest syntax (describe, it, expect) consistent with the project configuration in jest.config.ts.

Exercise 5.4: Apply Tests and Re-measure (Optional)

Apply the generated tests and measure the coverage improvement.

1. Copy the generated test code into a new file:

   # Create the test file (paste the generated content)
   code sample-app/__tests__/utils.test.ts
   

2. Save the file with the generated test content from Exercise 5.3.

3. Re-run the test suite with coverage:

   cd sample-app
   npm test -- --coverage
   

4. Compare the new coverage percentage to the baseline from Exercise 5.1. You should see a measurable improvement in the coverage for src/lib/utils.ts.
5. This exercise demonstrates the detect → generate → verify cycle from Lab 02: the Code Quality Detector identified the gap, the Test Generator produced tests, and re-running coverage confirms the improvement.

Verification Checkpoint

Before proceeding, verify:

• You measured the baseline test coverage (approximately 5%)
• The code-quality-detector identified low coverage, complexity, or type safety issues
• The test-generator produced unit tests for utils.ts
• (Optional) You applied the generated tests and observed improved coverage
• You understand the detect → generate → verify cycle for code quality

Next Steps

Proceed to Lab 06.