Coding Bolt

Traditional testing methodologies, like unit testing, while essential, they do not provide a comprehensive assessment of your test suite’s effectiveness. This is where mutation testing and tools like Stryker come into play. With mutation testing you can basically check the healthiness of your tests!

What is Mutation Testing?

Mutation testing is a technique used to evaluate the effectiveness of your existing test suite. The idea revolves around introducing small, deliberate changes (mutations) to your code and then running your tests to see if they catch these alterations. For you example, it removes a line of code or changes an equals operator to a not equals. If a test fails due to the mutation, it’s considered effective. Conversely, if the tests pass despite the mutation, it indicates gaps in your tests. In a nutshell, you test your tests!

Why Mutation Testing?

• Assess Test Suite Effectiveness: Mutation testing goes beyond code coverage metrics. Covering a lot of code but in a wrong way, does nothing at the end of the day.
• Improve Code Quality: By identifying weaknesses in your tests, you can bolster them to better safeguard against bugs and regressions.
• Facilitate Refactoring: A strong test suite, gives developers the confidence to refactor code without fear of introducing new issues.

What is Stryker?

Stryker is a powerful mutation testing framework designed to integrate seamlessly into modern development workflows. Initially developed for JavaScript, Stryker has expanded its support to multiple languages, including TypeScript, Java, C#, and more.

Key Features of Stryker

• Integration with CI/CD: Stryker can be integrated into continuous integration and deployment pipelines providing feedback instantly.
• Customizable Mutation Operators: You can choose the types of mutations Stryker introduces to align with your project’s specific needs.
• Detailed Reports: Stryker generates comprehensive reports that highlight which mutations were killed and which survived.

Installation and run

First, install Stryker.NET as a global tool using the .NET CLI:

dotnet tool install -g dotnet-stryker

Navigate to the project directory and execute the mutation testing process with:

dotnet stryker

Stryker.NET will perform the mutations, run your tests against each mutant, and generate a report highlighting the results.

Interpreting Stryker.NET’s Reports

Stryker.NET provides detailed reports that typically include:

• Mutation Score: The percentage of mutants killed by your tests. A higher score indicates a more effective test suite.
• Survived Mutants: Mutants that weren’t detected by tests, signaling potential gaps.
• Error Mutants: Cases where the mutation process failed, often due to unsupported code patterns or issues in the codebase.
• Killed Mutants: Successfully detected mutations, showcasing the strengths of your tests.

For more detailed information you can visit: Introduction | Stryker Mutator (stryker-mutator.io)

Conclusion

Keeping your .NET projects in top shape doesn’t have to be a chore. Stryker.NET makes mutation testing accessible and straightforward, giving you a clear picture of how solid your tests really are. Think of it as a friendly check-up for your code—spotting those sneaky gaps before they become bigger issues.

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