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orbit-qa-mutation
GitHub基于 Infection 的 PHP 变异测试工具，用于评估测试质量而非代码质量。通过修改代码行并运行测试套件，检测未覆盖的潜在 Bug。MSI 越高表示测试越有效。
Trigger Scenarios
mutation testing
Infection PHP
test quality
are my tests good
Install
npx skills add NeverSight/learn-skills.dev --skill orbit-qa-mutation -g -y
SKILL.md
Frontmatter
{
"name": "orbit-qa-mutation",
"description": "Mutation testing for PHP via Infection — measures TEST quality (not code quality). Mutates each line of code (e.g. `<` → `<=`, `&&` → `||`) and runs the test suite. If tests still pass, the mutation \"survived\" = the test missed the bug. Higher kill rate = better tests. Use when the user says \"mutation testing\", \"Infection PHP\", \"test quality\", \"are my tests good\"."
}
🪐 orbit-qa-mutation — Infection PHP mutation testing
Tests can pass while having gaping holes. Mutation testing is the test-quality test: deliberately break code, see if tests notice.
Quick start
# Install once
composer require --dev infection/infection
# Run
vendor/bin/infection --threads=4
Output: infection.log + reports/mutation-<timestamp>.md.
What "mutation" means
Infection rewrites each line of your PHP — small, deterministic changes:
// Original
if ($price > 100) { return true; }
// Mutation 1: `>` → `<`
if ($price < 100) { return true; }
// Mutation 2: `>` → `>=`
if ($price >= 100) { return true; }
// Mutation 3: `true` → `false`
if ($price > 100) { return false; }
// Mutation 4: `100` → `0`
if ($price > 0) { return true; }
For each mutation, Infection runs your test suite. If any test fails → mutation "killed." If all pass → mutation "survived." Survived mutations = a real bug your tests would miss.
Mutation Score Indicator (MSI)
MSI (Mutation Score Indicator) = killed / total mutations
| MSI | Verdict |
|---|---|
| 90%+ | Excellent — tests truly cover behaviour |
| 70-89% | Good |
| 50-69% | Mediocre — tests check existence, not behaviour |
| < 50% | Tests probably just check "doesn't crash" |
Configure for a WP plugin
infection.json5:
{
"$schema": "https://raw.githubusercontent.com/infection/infection/0.27.0/resources/schema.json",
"source": { "directories": ["src", "includes"] },
"phpUnit": { "configDir": "tests" },
"logs": {
"text": "infection.log",
"html": "reports/mutation.html"
},
"mutators": {
"@default": true,
"@cast": false, // skip type-casting mutations (noisy in WP)
"@regex": false // skip regex mutations (noisy)
},
"minMsi": 70,
"minCoveredMsi": 80
}
minMsi and minCoveredMsi are CI gates — fail the build if score drops.
Common survived mutations
Off-by-one
// Original — `<=` (inclusive)
for ($i = 0; $i <= count($items); $i++)
// Mutation: `<=` → `<` (exclusive — drops last item)
for ($i = 0; $i < count($items); $i++)
If tests don't cover the boundary case (last item), mutation survives.
Boolean inversion
if ( ! current_user_can( 'manage_options' ) ) wp_die();
// Mutation: drop the !
if ( current_user_can( 'manage_options' ) ) wp_die();
If tests don't try a permitted user expecting success AND a denied user expecting fail, mutation survives.
Default value
$value = get_option( 'my_setting', 'default' );
// Mutation: 'default' → ''
$value = get_option( 'my_setting', '' );
If tests don't run with the option missing, mutation survives.
Output
# Mutation Testing — my-plugin
Mutations: 1,247
Killed: 1,082 (87%)
Survived: 165 (13%)
Timed out: 0
Skipped: 0
MSI: 87% — Good (target: 90%)
## Top survived mutations (suggested test additions)
- src/class-cart.php:47 — boolean inversion
→ Add test: anonymous user CAN'T add to cart
- src/class-checkout.php:103 — off-by-one in loop
→ Add test: 0-item cart, 1-item cart, max-items cart
- src/class-pricing.php:88 — default fallback
→ Add test: option deleted, expect $0.00 not 'free'
Pair with
/orbit-qa-coverage— line coverage (mutation testing IS quality of coverage)/orbit-wp-standards— clean code easier to mutate-test
Sources & Evergreen References
Canonical docs
- Infection PHP — root
- Infection Configuration — config reference
- Mutation Testing — Wikipedia — theory
- Stryker Mutator — JS / TS mutation testing
Rule lineage
- Mutation testing — academic since 1971, practical PHP since Infection 0.x (~2017)
- Infection 1.0 — 2024
Last reviewed
- 2026-04-29
Version History
- e0220ca Current 2026-07-05 23:23
