Fastest Way to Understand Stryker

The article provides a step-by-step guide to setting up a .NET solution with a console app, class library, and xUnit test project, then demonstrates how to install and run the Stryker mutation testing tool. It shows how Stryker introduces code mutations (e.g., changing `a + b` to `a - b`) and identifies whether tests fail, revealing weak tests that pass but don't properly verify behavior. The article concludes by noting that mature engineering teams integrate Stryker into CI/CD pipelines (e.g., GitHub Actions) to enforce high mutation scores.

FASTEST WAY TO UNDERSTAND STRYKER We'll create: Console App ↓ Class Library ↓ Unit Test Project ↓ Run Stryker You’ll understand: - solution structure - testing flow - mutation testing - enterprise-level quality tooling STEP 1 - Create Solution Open terminal: mkdir StrykerDemo cd StrykerDemo dotnet new sln STEP 2 - Create Class Library This contains business logic. dotnet new classlib -n StrykerDemo.Core Add to solution: dotnet sln add StrykerDemo.Core STEP 3 - Create Test Project Use xUnit. dotnet new xunit -n StrykerDemo.Tests Add to solution: dotnet sln add StrykerDemo.Tests Reference Core project: dotnet add StrykerDemo.Tests reference StrykerDemo.Core STEP 4 - Create Actual Logic Inside: StrykerDemo.Core Create: namespace StrykerDemo.Core; public class Calculator { public int Add int a, int b { return a + b; } } STEP 5 - Create Unit Test Inside test project: using StrykerDemo.Core; namespace StrykerDemo.Tests; public class CalculatorTests { Fact public void Add Should Return Correct Value { var calculator = new Calculator ; var result = calculator.Add 2, 3 ; Assert.Equal 5, result ; } } STEP 6 - Verify Tests Run: dotnet test You should see: Passed STEP 7 - Install Stryker Install globally: dotnet tool install -g dotnet-stryker Verify: dotnet stryker --version STEP 8 — RUN STRYKER Go to test project: cd StrykerDemo.Tests Run: dotnet stryker WHAT HAPPENS NOW Stryker will: - Find your code - Mutate it - Run tests repeatedly Example mutation: Original: a + b Mutated: a - b Your test expects: 5 Mutated result: -1 Test fails. Mutation killed ✅ NOW LET’S SEE A SURVIVING MUTATION Change test to weak test: Assert.True result 0 ; instead of: Assert.Equal 5, result ; Now rerun Stryker. Some mutations may survive because: - subtraction may still return positive - your assertion is too generic THIS is where mutation testing becomes powerful. Viewing the Stryker HTML Report After running: dotnet stryker Stryker automatically generates an HTML report inside: StrykerOutput/<timestamp /reports/mutation-report.html Example: StrykerOutput/2026-05-23.14-56-48/reports/mutation-report.html You can also automatically open the report in your browser: dotnet stryker --open-report or dotnet stryker -o THE BIG ENTERPRISE INSIGHT In real enterprise systems: - code coverage can say 90% - but mutation score may say 40% Meaning: tests execute code but don’t truly verify behavior. That’s why mature engineering teams use: - unit tests - integration tests - mutation testing - quality gates in CI/CD HOW THIS LOOKS IN GITHUB Usually: GitHub Actions ↓ dotnet test ↓ dotnet stryker ↓ Fail pipeline if mutation score low This is where you begin seeing: - real engineering ownership - architecture visibility - DevOps quality flow - not just user story implementation WHAT YOU SHOULD DO NEXT After this basic example: - Add more methods - Add edge cases - Purposely create weak tests - Watch mutations survive - Improve tests - Re-run Stryker That loop teaches more than tutorials.