Generate tests for existing code

Follow these guidelines when you need to create comprehensive test coverage for existing functions or classes.

• Time estimate: 10-20 minutes
• Level: Beginner
• Prerequisites: Code file open in IDE, GitLab Duo Chat available, existing code to test

The challenge

Create thorough test coverage for existing code without manually writing boilerplate test cases and setup code.

The approach

Select code, generate tests, and refine coverage by using GitLab Duo Chat and Code Suggestions.

Step 1: Generate

Select the function or class you want to test, then use GitLab Duo Chat to generate tests.

Generate tests for the selected [function_name/ClassName] by using [test_framework]:

1. Include test cases for normal operation
2. Add edge cases and error conditions
3. Test boundary values and invalid inputs
4. Follow [testing_conventions] for our project
5. Include setup and teardown if needed

Make the tests comprehensive but readable.

Expected outcome: Complete test file with multiple test cases covering different scenarios.

Step 2: Refine

Review the generated tests and ask for specific improvements.

Review the generated tests and:
1. Add any missing edge cases for [specific_functionality]
2. Improve test names to be more descriptive
3. Add comments explaining complex test scenarios
4. Ensure tests follow [specific_style_guide]

Focus on making tests maintainable and clear.

Expected outcome: Polished test file with clear, comprehensive coverage.

Step 3: Extend

Use Code Suggestions to add additional test cases. Type this text in your file.

// Test [specific_edge_case_scenario]
// Test [error_condition]
// Test [boundary_condition]

Expected outcome: Code Suggestions helps complete additional test cases.

Tips

• Select specific functions or classes rather than entire files for better results.
• Be specific about your testing framework (for example, Jest, pytest, RSpec).
• Ask Chat to explain the reasoning behind test cases if you're learning.
• Use Code Suggestions to quickly add similar test patterns.
• Request both positive and negative test cases for thorough coverage.

Verify

Ensure that:

• Tests cover the main functionality and common edge cases.
• Test names clearly describe what is being tested.
• Tests follow your project's testing conventions and style.
• All tests pass when run against the existing code.