Mutatest vs PIT

Mutatest is a free command-line tool for Python projects that checks whether tests catch small changes to code. It creates valid mutations from Python’s Abstract Syntax Tree grammar and applies them to local __pycache__ files rather than changing source files. If coverage data is available, it can limit targets to lines marked as covered. Mutations are sampled randomly, with a seed available to make runs reproducible. Command-line controls include run modes, mutation categories, file exclusions, timeouts, reports, and thresholds for surviving mutants; an API supports custom controls. The documentation describes using test commands such as pytest and coverage data to filter targets. Mutatest can raise an exception when surviving mutants meet a configured threshold, including in automated runs such as CI. It supports Linux, macOS, and Windows, and is free under the MIT License. Installation requires Python 3.7 or 3.8; multiprocessing is available on 3.8, but not 3.7. Repeated test runs can be slow, so it is intended for diagnostics rather than every commit across an entire codebase.

PIT is a free mutation-testing tool for Java and JVM bytecode projects. It measures whether unit tests detect faults by running them against modified versions of application code. Configurable bytecode mutations can remove method calls, invert logic, or change return values. PIT selects and prioritizes tests using line coverage, execution speed, and naming conventions, then reports mutation coverage alongside line coverage. It can run from the command line, Ant, or Maven; third-party integrations are listed for Gradle, Eclipse, and IntelliJ. Java is supported directly, and Kotlin use is available through the ArcMutate plugin. PIT supports JUnit 3, JUnit 4, and TestNG; JUnit 5 needs a plugin. Versions 1.4.0 and later require Java 8 or above and JUnit or TestNG on the classpath. Mutation runs can take a long time depending on codebase size and test-suite speed, so PIT recommends focusing on changed code. It mutates bytecode and requires line numbers and source file names in that bytecode.