How is Aggregate Code Coverage Calculated in Salesforce?

Question:

Imagine a Salesforce org with two classes and their respective test coverage statistics:

Class 1: 400 testable lines, 200 covered  
Class 2: 10 testable lines, 10 covered  

How is aggregate test coverage calculated for the org? Does Salesforce determine the coverage by averaging the percentages for each class (e.g., Class 1: 50%, Class 2: 100%, average = 75%), or does it calculate the coverage as the ratio of all covered lines to all testable lines in the org (e.g., (200 + 10) / (400 + 10) = 51.2%)?

The distinction matters because the result could significantly affect deployment readiness. If the average method is used, the coverage in this example is 75%, which exceeds the required 75% for production deployments. However, if the total line ratio method is used, the coverage is 51.2%, which does not meet the threshold.

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Answer:

Salesforce calculates aggregate code coverage using the total line ratio method, not the average of class percentages. This means the overall test coverage is determined by summing the number of covered lines across all classes and dividing it by the total number of testable lines in the org.

In the given example:

Covered lines: 200 (Class 1) + 10 (Class 2) = 210  
Total lines: 400 (Class 1) + 10 (Class 2) = 410  
Coverage = 210 / 410 ≈ 51.2%  

Since the total coverage is below 75%, the org would not meet the requirement for production deployment.

This method reflects the principle that larger classes with many uncovered lines have a more significant impact on aggregate coverage than smaller classes, regardless of their individual percentages.

Why the Line Ratio Method Matters

The line ratio method ensures fairness and focuses on improving the overall quality of code in the org, rather than allowing smaller classes with perfect coverage to offset larger, poorly tested classes. For example:

• Adding a single covered line in a small class with 10 lines (to increase its coverage from 90% to 100%) would have a negligible impact on overall coverage.
• On the other hand, adding 10 covered lines in a large class with 400 lines could significantly improve the aggregate coverage.

Strategy for Increasing Coverage

When working to meet deployment requirements, focus on:

Larger Classes:

These have more testable lines, and covering edge cases or missing branches will likely increase coverage significantly.

Critical Code Paths:

Ensure that the most important business logic is fully covered.

Low-Hanging Fruit:

Easy-to-test code, such as simple methods or utility functions, can provide a quick boost

Code Reviews:

Identify areas where untested code can be covered efficiently.

Understanding Salesforce’s emphasis on total testable lines ensures that your efforts to improve test coverage are both effective and aligned with deployment requirements.

Summing Up

Aggregate code coverage in Salesforce is calculated using the total line ratio method, where the ratio of all covered lines to all testable lines in the org determines the overall coverage. This method ensures that the focus remains on improving the quality of code across the entire org, as larger classes with more untested lines carry greater weight than smaller, fully-covered classes. Unlike averaging class percentages, the line ratio method reflects the actual testing completeness of your org’s codebase, providing a fair and accurate representation of coverage.

For teams working to meet the 75% coverage requirement for production deployments, prioritizing larger classes, critical business logic, and easy-to-test methods can yield better results. This approach not only improves aggregate coverage but also enhances the maintainability and reliability of your org’s code. Understanding this calculation method allows developers to strategically address coverage gaps and deploy confidently to production.

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