InfectionPHP Mutation Testing Framework

Find the tests you are missing. Infection mutates your source code and tells you which changes your test suite fails to catch.

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Adopted across the PHP ecosystem

The standard for mutation testing in PHP

Infection is the tool the PHP community reaches for when line coverage stops being convincing — used by frameworks, libraries and application teams to prove their tests actually assert something.

33.9M+: installs to date 33,937,286 via Composer
1.8M: installs a month about 76,123 every day
2,521: packages depend on it listed as a dependency on Packagist
2,259: stars on GitHub infection/infection

Source: packagist.org/packages/infection/infection — as of 2026-10-14

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Mutation Testing, not coverage

Line coverage only proves a line was executed. Infection changes the code under test and reports the mutations your suite still passes on — the gaps coverage cannot see.

How it works

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Mutation Score Indicator

A single number for test-suite quality, enforceable in CI with --min-msi and --min-covered-msi, and publishable as a badge on your README. Measures the quality of the tests. Fail builds.

MSI and badges

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Built for real test suites

Parallel runs, reuse of existing coverage, and --git-diff-lines to mutate only what a pull request touched — so mutation testing fits inside a normal build.

Command line options

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Works with your stack

PHPUnit, Codeception and PHPSpec, with 100+ mutators grouped into profiles, custom mutators, and static analysis integration.

Supported frameworks