Pull Request Coverage

Pull Request Coverage refers to the analysis and reporting of code coverage metrics specifically within the context of pull requests (PRs). This process helps teams assess the test quality of proposed changes before they are merged into the main codebase, ensuring that new code meets established quality standards.

Components of Pull Request Coverage

Pull request coverage analysis typically includes several distinct metrics:

• Patch Coverage: The percentage of new or modified lines in the PR that are covered by tests
• Coverage Change: How the PR affects the overall coverage percentage of the codebase
• Total Coverage: The resulting overall coverage if the PR is merged
• Uncovered Lines: Specific identification of new or modified lines that lack test coverage
• Quality Metrics: Additional code quality indicators like complexity changes or CRAP scores

How Pull Request Coverage Works

The process of analyzing and reporting PR coverage involves several steps:

1. Base Analysis: Establishing baseline coverage metrics from the target branch
2. Change Detection: Identifying which files and lines have been modified in the PR
3. Test Execution: Running tests against the PR code with coverage instrumentation
4. Differential Analysis: Comparing coverage results with the baseline
5. Reporting: Presenting results in a format that helps reviewers assess code quality
6. Status Updates: Updating PR status based on whether coverage meets defined thresholds

Benefits of Pull Request Coverage

Implementing PR coverage analysis offers numerous advantages:

• Early Feedback: Identifies coverage issues before code is merged
• Quality Enforcement: Creates a quality gate that helps maintain or improve code standards
• Focused Review: Directs reviewers' attention to potentially problematic areas
• Developer Awareness: Raises developers' awareness of test coverage during development
• Incremental Improvement: Enables gradual enhancement of overall code quality
• Objective Evaluation: Provides data-driven insights rather than subjective impressions

Integration with Code Review Workflow

Pull request coverage can be integrated into the code review process in several ways:

• Status Checks: Using GitHub status checks to block merging when coverage thresholds aren't met
• Automated Comments: Adding comments to PRs with coverage information and highlighting uncovered code
• Visual Indicators: Providing color-coded visualizations of coverage in the diff view
• Coverage Reports: Linking to detailed coverage reports for deeper analysis
• Review Guidelines: Incorporating coverage review into formal code review processes

Setting Coverage Requirements

Organizations often establish specific requirements for pull request coverage:

• Minimum Patch Coverage: Requiring high coverage (often 80-100%) for changed lines
• No Coverage Decrease: Preventing PRs from reducing the overall coverage percentage
• Context-Specific Standards: Applying different standards to different parts of the codebase
• Exception Processes: Establishing mechanisms for justified exceptions to coverage requirements

Pull Request Coverage in OtterWise

OtterWise provides comprehensive pull request coverage analysis:

• PR Comments: Detailed coverage information automatically added to pull requests
• Status Checks: GitHub status checks based on configurable coverage thresholds
• Line Annotations: Visual indicators showing which specific lines lack coverage
• Detailed Reports: In-depth coverage information accessible via links in the PR
• Historical Comparison: Tracking how coverage changes over time across multiple PRs

Pull request coverage analysis is a critical tool for maintaining and improving code quality in modern development workflows. By making test coverage a visible part of the code review process, teams can ensure that new code meets quality standards while gradually improving the overall health of the codebase.