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Infection
What it is
Infection is a free PHP mutation-testing library that checks whether a test suite catches changes to source code. It creates altered versions of code, runs tests that cover the changed lines, and records detected and surviving mutations, errors, and timeouts. Its Mutation Score Indicator measures the share of generated mutations detected by tests; it also reports Mutation Code Coverage and Covered Code Mutation Score Indicator. Infection runs from a project root as a CLI tool and supports PHPUnit, PhpSpec, Codeception, and Testo. Teams can run mutated tests in parallel, limit analysis to changed lines or files, and configure minimum scores that fail a build. The project describes more than 100 mutators, supports custom mutators, and offers optional PHPStan and Mago integrations. A browser playground lets users run mutation testing on PHP code and tests without installing the tools locally. Current documentation requires PHP 8.3 or newer and Xdebug, phpdbg, or pcov. Installation methods include PHAR, Phive, Composer, Git, and Homebrew. It is released under the BSD-3-Clause license.
For and against
For
- Supports PHPUnit, PhpSpec, Codeception, and Testo.
- Can restrict mutation analysis to changed lines or files.
- Score thresholds can fail a build.
- Includes a browser playground for PHP mutation testing.
- Available through several installation methods.
Against
- Requires PHP 8.3 or newer.
- Requires Xdebug, phpdbg, or pcov.
- Parallel runs may give false positives with dependent or database-using tests.
- Security support focuses on the latest version.
The verdict
Infection offers several ways to focus and measure mutation testing in PHP projects, including changed-code analysis and build thresholds. Check its runtime requirements and parallel-run caveat before adopting it.
Who it suits
Infection suits PHP developers who want to assess whether tests detect code changes, including teams using one of its supported test frameworks. Its changed-code modes and score thresholds may be useful for incremental analysis and build checks.
On the record
- Browser playground
- The Infection Playground lets users write PHP code and tests in a browser and run mutation testing without installing Composer, Infection, or PHPUnit.infection.github.io · read 2 Oct 2026
- Caveat
- The command-line guide warns that parallel runs can produce false positives when tests depend on one another or use a database.infection.github.io · read 2 Oct 2026
- Changed-code mode
- The --git-diff-lines option mutates only touched lines, and --git-diff-filter can restrict mutation to changed files.infection.github.io · read 30 Sep 2026
- CI reports
- Infection can emit GitHub annotations and GitLab Code Quality reports, and can publish mutation badges and HTML reports through Stryker Dashboard.infection.github.io · read 2 Oct 2026
- CI thresholds
- The --min-msi and --min-covered-msi options can fail a build when the configured mutation-score threshold is not met.infection.github.io · read 2 Oct 2026
- Cloud reporting
- Infection can send mutation badges and HTML reports to Stryker Dashboard using a project API key.infection.github.io · read 30 Sep 2026
- Community support
- The project links to Discord and GitHub Discussions for community help and states that it welcomes pull requests and issues.github.com · read 30 Sep 2026
- Distribution
- The recommended PHAR distribution bundles PHPUnit, PhpSpec, Codeception and Testo, and the PHAR signature can be verified with the documented GPG key.infection.github.io · read 30 Sep 2026
- How it works
- It creates mutants using predefined mutation operators, runs tests covering changed lines, and records killed or escaped mutants, errors, and timeouts.infection.github.io · read 2 Oct 2026
- Installation
- The maker documents PHAR, Phive, Composer, Git, and Homebrew installation methods.infection.github.io · read 2 Oct 2026
- License
- The project is released under the BSD-3-Clause License.infection.github.io · read 2 Oct 2026
- Mutation metrics
- Infection provides Mutation Score Indicator, Mutation Code Coverage and Covered Code Mutation Score Indicator metrics.infection.github.io · read 30 Sep 2026
- Mutation score
- It reports a Mutation Score Indicator (MSI) that measures the percentage of generated mutations detected by the tests.infection.github.io · read 2 Oct 2026
- Mutators
- The homepage describes more than 100 mutators, grouped into profiles, and support for custom mutators.infection.github.io · read 2 Oct 2026
- Parallel execution
- Tests for mutated code can run in parallel with the --threads option, including automatic CPU-core detection with --threads=max.infection.github.io · read 30 Sep 2026
- Purpose
- Infection mutates PHP source code and reports changes that a test suite fails to catch.infection.github.io · read 2 Oct 2026
- Runtime requirements
- The current guide says Infection requires PHP 8.3 or later and Xdebug, phpdbg, or pcov installed.infection.github.io · read 2 Oct 2026
- Security
- The maker says its PHAR distribution is signed with a GPG key and documents how to verify the signature and fingerprint.infection.github.io · read 2 Oct 2026
