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mutation-testing

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Original

English
🇨🇳

Translation

Chinese

Mutation Testing

突变测试

<default_to_action> When validating test quality or improving test effectiveness:
  1. MUTATE code (change + to -, >= to >, remove statements)
  2. RUN tests against each mutant
  3. VERIFY tests catch mutations (kill mutants)
  4. IDENTIFY surviving mutants (tests need improvement)
  5. 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>
<default_to_action> 在验证测试质量或提升测试有效性时：
  1. 对代码进行突变（将+改为-，>=改为>，移除语句等）
  2. 针对每个突变体运行测试
  3. 验证测试是否能捕获突变（杀死突变体）
  4. 识别存活的突变体（对应的测试需要改进）
  5. 强化测试以杀死存活的突变体
快速突变指标：
  • 突变分数 = 被杀死的突变体数量 / (被杀死的突变体数量 + 存活的突变体数量)
  • 目标：突变分数 > 80%
  • 存活的突变体 = 薄弱的测试
关键成功要素：
  • 高覆盖率 ≠ 优质测试（100%覆盖率但0%断言）
  • 突变测试可证明测试确实能发现漏洞
  • 优先关注关键代码路径 </default_to_action>

Quick Reference Card

快速参考卡

When to Use

使用场景

  • Evaluating test suite quality
  • Finding gaps in test assertions
  • Proving tests catch bugs
  • Before critical releases
  • 评估测试套件质量
  • 发现测试断言中的漏洞
  • 证明测试能发现漏洞
  • 关键版本发布前

Mutation Score Interpretation

突变分数解读

ScoreInterpretation
90%+Excellent test quality
80-90%Good, minor improvements
60-80%Needs attention
< 60%Significant gaps
分数解读
90%+测试质量极佳
80-90%良好，需小幅改进
60-80%需要关注
< 60%存在重大漏洞

Common Mutation Operators

常见突变操作符

CategoryOriginalMutant
Arithmetic
a + b
a - b
Relational
x >= 18
x > 18
Logical
a && b
a || b
Conditional
if (x)
if (true)
Statement
return x
(removed)
类别原代码突变体
算术运算
a + b
a - b
关系运算
x >= 18
x > 18
逻辑运算
a && b
a || b
条件判断
if (x)
if (true)
语句移除
return x
(已移除)

How Mutation Testing Works

突变测试的工作原理

javascript
// Original code
function isAdult(age) {
  return age >= 18; // ← Mutant: change >= to >
}

// Strong test (catches mutation)
test('18 is adult', () => {
  expect(isAdult(18)).toBe(true); // Kills mutant!
});

// Weak test (mutation survives)
test('19 is adult', () => {
  expect(isAdult(19)).toBe(true); // Doesn't catch >= vs >
});
// Surviving mutant → Test needs boundary value
javascript
// Original code
function isAdult(age) {
  return age >= 18; // ← Mutant: change >= to >
}

// Strong test (catches mutation)
test('18 is adult', () => {
  expect(isAdult(18)).toBe(true); // Kills mutant!
});

// Weak test (mutation survives)
test('19 is adult', () => {
  expect(isAdult(19)).toBe(true); // Doesn't catch >= vs >
});
// Surviving mutant → Test needs boundary value

Using Stryker

使用Stryker

bash
undefined
bash
undefined

Install

Install

npm install --save-dev @stryker-mutator/core @stryker-mutator/jest-runner
npm install --save-dev @stryker-mutator/core @stryker-mutator/jest-runner

Initialize

Initialize

npx stryker init

**Configuration:**
```json
{
  "packageManager": "npm",
  "reporters": ["html", "clear-text", "progress"],
  "testRunner": "jest",
  "coverageAnalysis": "perTest",
  "mutate": [
    "src/**/*.ts",
    "!src/**/*.spec.ts"
  ],
  "thresholds": {
    "high": 90,
    "low": 70,
    "break": 60
  }
}
Run:
bash
npx stryker run
Output:
Mutation Score: 87.3%
Killed: 124
Survived: 18
No Coverage: 3
Timeout: 1
npx stryker init

**配置：**
```json
{
  "packageManager": "npm",
  "reporters": ["html", "clear-text", "progress"],
  "testRunner": "jest",
  "coverageAnalysis": "perTest",
  "mutate": [
    "src/**/*.ts",
    "!src/**/*.spec.ts"
  ],
  "thresholds": {
    "high": 90,
    "low": 70,
    "break": 60
  }
}
运行：
bash
npx stryker run
输出：
Mutation Score: 87.3%
Killed: 124
Survived: 18
No Coverage: 3
Timeout: 1

Fixing Surviving Mutants

修复存活的突变体

javascript
// Surviving mutant: >= changed to >
function calculateDiscount(quantity) {
  if (quantity >= 10) { // Mutant survives!
    return 0.1;
  }
  return 0;
}

// Original weak test
test('large order gets discount', () => {
  expect(calculateDiscount(15)).toBe(0.1); // Doesn't test boundary
});

// Fixed: Add boundary test
test('exactly 10 gets discount', () => {
  expect(calculateDiscount(10)).toBe(0.1); // Kills mutant!
});

test('9 does not get discount', () => {
  expect(calculateDiscount(9)).toBe(0); // Tests below boundary
});
javascript
// Surviving mutant: >= changed to >
function calculateDiscount(quantity) {
  if (quantity >= 10) { // Mutant survives!
    return 0.1;
  }
  return 0;
}

// Original weak test
test('large order gets discount', () => {
  expect(calculateDiscount(15)).toBe(0.1); // Doesn't test boundary
});

// Fixed: Add boundary test
test('exactly 10 gets discount', () => {
  expect(calculateDiscount(10)).toBe(0.1); // Kills mutant!
});

test('9 does not get discount', () => {
  expect(calculateDiscount(9)).toBe(0); // Tests below boundary
});

Agent-Driven Mutation Testing

Agent驱动的突变测试

typescript
// Analyze mutation score and generate fixes
await Task("Mutation Analysis", {
  targetFile: 'src/payment.ts',
  generateMissingTests: true,
  minScore: 80
}, "qe-test-generator");

// Returns:
// {
//   mutationScore: 0.65,
//   survivedMutations: [
//     { line: 45, operator: '>=', mutant: '>', killedBy: null }
//   ],
//   generatedTests: [
//     'test for boundary at line 45'
//   ]
// }

// Coverage + mutation correlation
await Task("Coverage Quality Analysis", {
  coverageData: coverageReport,
  mutationData: mutationReport,
  identifyWeakCoverage: true
}, "qe-coverage-analyzer");
typescript
// Analyze mutation score and generate fixes
await Task("Mutation Analysis", {
  targetFile: 'src/payment.ts',
  generateMissingTests: true,
  minScore: 80
}, "qe-test-generator");

// Returns:
// {
//   mutationScore: 0.65,
//   survivedMutations: [
//     { line: 45, operator: '>=', mutant: '>', killedBy: null }
//   ],
//   generatedTests: [
//     'test for boundary at line 45'
//   ]
// }

// Coverage + mutation correlation
await Task("Coverage Quality Analysis", {
  coverageData: coverageReport,
  mutationData: mutationReport,
  identifyWeakCoverage: true
}, "qe-coverage-analyzer");

Agent Coordination Hints

Agent协作提示

Memory Namespace

内存命名空间

aqe/mutation-testing/
├── mutation-results/*   - Stryker reports
├── surviving/*          - Surviving mutants
├── generated-tests/*    - Tests to kill mutants
└── trends/*             - Mutation score over time
aqe/mutation-testing/
├── mutation-results/*   - Stryker reports
├── surviving/*          - Surviving mutants
├── generated-tests/*    - Tests to kill mutants
└── trends/*             - Mutation score over time

Fleet Coordination

集群协作

typescript
const mutationFleet = await FleetManager.coordinate({
  strategy: 'mutation-testing',
  agents: [
    'qe-test-generator',     // Generate tests for survivors
    'qe-coverage-analyzer',  // Coverage correlation
    'qe-quality-analyzer'    // Quality assessment
  ],
  topology: 'sequential'
});
typescript
const mutationFleet = await FleetManager.coordinate({
  strategy: 'mutation-testing',
  agents: [
    'qe-test-generator',     // Generate tests for survivors
    'qe-coverage-analyzer',  // Coverage correlation
    'qe-quality-analyzer'    // Quality assessment
  ],
  topology: 'sequential'
});

Related Skills

相关技能

  • tdd-london-chicago - Write effective tests first
  • test-design-techniques - Boundary value analysis
  • quality-metrics - Measure test effectiveness
  • tdd-london-chicago - 先编写有效的测试
  • test-design-techniques - 边界值分析
  • quality-metrics - 评估测试有效性

Remember

注意事项

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.
高代码覆盖率 ≠ 优质测试。100%覆盖率但断言薄弱的测试毫无用处。突变测试可证明测试确实能发现漏洞。
优先关注关键路径。无需对所有代码进行突变测试，优先处理支付、认证、数据完整性相关代码。
借助Agent： Agent可运行突变分析、识别存活的突变体，并生成缺失的测试用例来杀死它们，实现测试质量的自动化提升。