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mutation-testing Test quality validation through mutation testing, assessing test suite effectiveness by introducing code mutations and measuring kill rate. Use when evaluating test quality, identifying weak tests, or proving tests actually catch bugs.
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GitHub リポジトリを開く name mutation-testing description Test quality validation through mutation testing, assessing test suite effectiveness by introducing code mutations and measuring kill rate. Use when evaluating test quality, identifying weak tests, or proving tests actually catch bugs. category specialized-testing priority high tokenEstimate 900 agents ["qe-test-generator","qe-coverage-analyzer","qe-quality-analyzer"] implementation_status optimized optimization_version 1 last_optimized 2025-12-02T00:00:00.000Z dependencies [] quick_reference_card true tags ["mutation","stryker","test-quality","kill-rate","assertions","effectiveness"]
Mutation Testing
<default_to_action>
When validating test quality or improving test effectiveness:
MUTATE code (change + to -, >= to >, remove statements)
RUN tests against each mutant
VERIFY tests catch mutations (kill mutants)
IDENTIFY surviving mutants (tests need improvement)
STRENGTHEN tests to kill surviving mutants
Quick Mutation Metrics:
Mutation Score = Killed / (Killed + Survived)
Target: > 80% mutation score
Surviving mutants = weak tests
Critical Success Factors:
High coverage ≠ good tests (100% coverage, 0% assertions)
Mutation testing proves tests actually catch bugs
Focus on critical code paths first
</default_to_action>
Quick Reference Card
When to Use
Evaluating test suite quality
Finding gaps in test assertions
Proving tests catch bugs
Before critical releases
Mutation Score Interpretation
Score Interpretation 90%+ Excellent test quality 80-90% Good, minor improvements 60-80% Needs attention < 60% Significant gaps
Common Mutation Operators
Category Original Mutant Arithmetic a + ba - bRelational x >= 18x > 18Logical a && ba || bConditional if (x)if (true)Statement return x(removed)
How Mutation Testing Works
function isAdult (age ) {
return age >= 18 ;
}
test ('18 is adult' , () => {
expect (isAdult (18 )).toBe (true );
});
test ('19 is adult' , () => {
expect (isAdult (19 )).toBe (true );
});
Using Stryker
npm install --save-dev @stryker-mutator/core @stryker-mutator/jest-runner
npx stryker init
{
"packageManager" : "npm" ,
"reporters" : [ "html" , "clear-text" , "progress" ] ,
"testRunner" : "jest" ,
"coverageAnalysis" : "perTest" ,
"mutate" : [
"src/**/*.ts" ,
"!src/**/*.spec.ts"
] ,
"thresholds" : {
"high" : 90 ,
"low" : 70 ,
"break" : 60
}
}
Mutation Score: 87.3%
Killed: 124
Survived: 18
No Coverage: 3
Timeout: 1
Fixing Surviving Mutants
function calculateDiscount (quantity ) {
if (quantity >= 10 ) {
return 0.1 ;
}
return 0 ;
}
test ('large order gets discount' , () => {
expect (calculateDiscount (15 )).toBe (0.1 );
});
test ('exactly 10 gets discount' , () => {
expect (calculateDiscount (10 )).toBe (0.1 );
});
test ('9 does not get discount' , () => {
expect (calculateDiscount (9 )).toBe (0 );
});
Agent-Driven Mutation Testing
await Task ("Mutation Analysis" , {
targetFile : 'src/payment.ts' ,
generateMissingTests : true ,
minScore : 80
}, "qe-test-generator" );
await Task ("Coverage Quality Analysis" , {
coverageData : coverageReport,
mutationData : mutationReport,
identifyWeakCoverage : true
}, "qe-coverage-analyzer" );
Agent Coordination Hints
Memory Namespace aqe/mutation-testing/
├── mutation-results/* - Stryker reports
├── surviving/* - Surviving mutants
├── generated-tests/* - Tests to kill mutants
└── trends/* - Mutation score over time
Fleet Coordination const mutationFleet = await FleetManager .coordinate ({
strategy : 'mutation-testing' ,
agents : [
'qe-test-generator' ,
'qe-coverage-analyzer' ,
'qe-quality-analyzer'
],
topology : 'sequential'
});
Related Skills
Remember High code coverage ≠ good tests. 100% coverage but weak assertions = useless. Mutation testing proves tests actually catch bugs.
Focus on critical paths first. Don't mutation test everything - prioritize payment, authentication, data integrity code.
With Agents: Agents run mutation analysis, identify surviving mutants, and generate missing test cases to kill them. Automated improvement of test quality.
